| Importance of Steel Reinforcement in Concrete Slab 2 |
| Posted By: Fundi Mjanja on 7th of November 2013 |
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The real questions become: How can one
guard against wide cracks and help maintain aggregate interlock, keeping
the slab in one plane?
The only answer is to use steel reinforcement. With concrete steel reinforcement the slab thickness is reduced by just replacing the strength of a thicker slab with the strength of the steel. Once there is a well-graded and compacted sub-base, one may want to consider the strength of steel reinforcement as contributing to the moment capacity of slabs and paving. Considerable area of steel reinforcement is necessary to provide structural support for the un-cracked concrete but when dealing with cracked concrete slabs and paving on grade (since the concrete is usually well supported uniformly) only properly positioned steel reinforcement in concrete will greatly improve the structural performance. To develop an area of steel for a reduced cross sectional area of slab or paving—say 1inch (25 mm) or 2 inches (50 mm) difference—we can use the difference in the cracking moments of two slab thicknesses and say the moment capacity of the steel reinforcement will replace the difference in the two moment capacities of the concrete. Even single layers of steel reinforcement will provide the reserve strength to maintain the thicker slab loading after the concrete cracks. As a bonus steel provides the necessary temperature and shrinkage protection as well as crack width control. It is also important to note that fewer control joints can be a consideration when steel reinforcement is used. Benefits of steel reinforced concrete slabs Here are the benefits of steel reinforced concrete slabs:
Finally admixtures are not an alternative to steel reinforcement as they both perform different roles in the concrete. Therefore, admixtures cannot be substituted for steel reinforcement and vice versa. The steel reinforcement industry is dedicated to providing quality steel reinforcement to the construction industry. It is essential to have a well-graded and compacted granular sub-base and the steel reinforcement sized, spaced, and placed properly. Of course, total quality can only be achieved when well qualified contractors and workmanship is employed on the construction site. |
Monday, 9 December 2013
Importance of Steel Reinforcement in Concrete Slab 2
Saturday, 7 December 2013
Importance of Steel Reinforcement in Concrete Slab
| Importance of Steel Reinforcement in Concrete Slab |
| Posted By: Fundi Mjanja on 31st of October 2013 |
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People
have most often misunderstood the importance of steel reinforcement in
concrete structures. Most laymen in the construction industry are
unaware that there is no substitute for concrete steel reinforcement in a
structural building.
The design/construction principal being responsible to the owners of the building project has a professional and moral responsibility to ensure that there are no substitutes for specified materials in the in the construction project. Contractor-Client conflicts over failures which arise because of plain concrete slabs are being reported more frequently than ever before. More often than not clients complain of being shortchanged by the contractors as they are not getting what was promised in the way of protection from wide cracks, the surface quality is poor and difficult to finish, and incurring excessive maintenance costs in repairing unravel joints and cracks. Clients end up spending a lot of money, either in tearing up and replacing with steel reinforced concrete or placing additional concrete topping to repair the poor quality surfaces. Concrete slab without reinforcement steel always result into extensive cracks over -time causing structural weakness. Concrete steel reinforcing has been in the construction marketplace over 100 years, and it has never disappointed whenever it is used properly. While most construction workers know that all steel reinforcement must be properly positioned in the concrete and be provided with sufficient cover, some steel ends up in the wrong place. In a slab on grade (ground slab on top of stable compacted hardcore fill) with one layer of reinforcement, the bar mats should be placed on supports which are 1/3 the depth from the top of the slab or a minimum concrete cover of at least 51 mm. Construction experts believe that the steel area should be reduced or terminated with slip steel dowels at construction joints to allow for free contraction and load transfer at those locations. This is a good measure especially where large concentrated loads are applied to floors. So what is wrong with just using plain concrete slabs and paving without incorporating reinforcement steel? All concrete will crack at some point due to some shrinkage that take place at control and construction joints, but many times you will find out that the slab has already “decided” to crack more randomly or at intermediate locations. If the steel reinforcement is left out and the sub-grade settles there is nothing to prevent the cracks from widening when the slab settles. |
Friday, 6 December 2013
Constructing on a sloppy Terrain
| Constructing on a sloppy Terrain |
| Posted By: Fundi Mjanja on 24th of October 2013 |
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Construction on a sloppy terrain can be a
really daunting task as it is complex and costly but the beauty of it is
that when the house is finally done you end up having a much more
interesting and beautiful house.
In this article we look at the implications of undertaking construction on a sloppy terrain. Costs The use of reinforced suspended concrete floors – most commonly precast beam – and hard landscaping, extra drainage, including perhaps the necessity for a pump, and extra work in stepping the foundations tend to be so costly. It is, however, questionable whether it is safe to try to extrapolate this into sliding scales or costs per square meter relating to degrees of slope — for instance 1% extra for every degree of slope. Cut and Fill This describes the process of carving out a level plinth on a sloping site, in order to build a home that is essentially designed for use on a level site. Any spoil that is cut from the bank is reserved in order for it to be brought back to make up the levels on the lower edge. The foundation costs are always going to increase due to the slope of the land and the requirement that the foundations should find original subsoil bearing. If the spoil is piled up against the lower or built up section of the new home then provision will have to be made for the over-site level within the building to be brought up to within 600mm of the proposed external soil level, in order to equalize the pressure on the walling. However, carting spoil away from a site is expensive and time consuming and its retention on site is a cost benefit, just so long as there is space to store it. Drainage and Sewers Having a sloping site may involve extra costs with drainage and sewers though not necessarily. In an instance where the site slopes down from a road in which the sewer is fairly shallow then the use a pumped sewage system may have to be employed in such a situation. In a scenario where the site slopes down from the road within which the sewer is quite deep, then the slope may actually represent a saving in cost, as the resulting house drainage will not have to be as deep. Sites which slope up from the road and sewer may seem to be more attractive as far as drainage is concerned, but if the slope is significant it might be necessary to install tumble bays within the manholes, in order to slow off the fall, so that the effluent can enter the sewer at a reasonable rate. Surface and rainwater is also a consideration. Sloping up from the road may at first seem the best option, but many local authorities will not allow surface water to go into the public sewers and many require that precautions are taken to ensure that surface water does not flow onto the road. Sloping down from the road means that surface water can collect around the base of the lower floor, or worse still find its way into the garage. This may mean having to install a drainage channel to divert the water to soak-away pits. Basements On a costing level a basement is always going to cost at least the same amount per square meter as any other part of the home, if not more. On ground with high water tables or in heavy clay, these costs and the sheer physical difficulties presented may make the choice unviable. However, if the lie of the land is such that there is no alternative to either a full or partial basement, then this can be the cost effective solution. Retaining Walls Basement walls will have to be strong enough to hold back considerable banks of ground, in which case they become retaining walls in their own right. In other situations, such as building on a level plinth beside a natural or carved out bank, it may be necessary to construct separate retaining walls above 1,200mm in height and these will have to be designed by an engineer. In certain circumstances it may be cheaper, and visually more attractive, to construct a series of lower retaining walls with the ground stepped between them. An alternative is wire cages – known as Gabions – filled with stone, or interlocking concrete blocks that are subsequently filled with soil and planted. Building On Stilts One way of building on steeply sloping land is to build on a series of supporting stilts or columns. This gets away from the need to build extensive foundations on sloping ground and it negates the need for tanking. It also leaves the ground relatively untouched, allowing planting to take place over much more of the site. In certain situations it can be the cost effective solution and there is no reason why it cannot be employed with multiple level designs. |
Wednesday, 4 December 2013
Managing Delays in Construction Projects – Contractor’s Approach
| Managing Delays in Construction Projects – Contractor’s Approach |
| Posted By: Fundi Mjanja on 17th of October 2013 |
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If
you are a Contractor involved in mechanical and electrical
installations then most probably you have struggled to deal with delays
in earlier phases of a project as a result of various factors that go
beyond your control.
One of the commonly used approach in such circumstances is the "Delay, Recover and Mitigate" (DRM) system. In order to deal with delays in construction or any other project for that matter and effectively apply the DRM approach one must be able to get early warning of delays that may be occasioned either the client, main contractor or the work force.
The Client If the client is cause of the delay then the contractor must make sure that client knows when they are the cause of the delay. It is very crucial to make this clear because many clients have “selective memories”. When they make design changes, issue late instructions, or are slow in approving designs, they need to realize that there is a knock on effect. Time is indeed money, and in this case it is the contractor's money unless it is recognized by the client what the effect of their actions is on the completion of the project stages. Use phrases such as "Mr Client, I am happy to implement these changes, however, I need to point out that we need to get your approvals before I implement these changes" and then get it in writing as a point of future reference incase the client may decide to pass the blame onto you in case the project fail to beat the delivery timeline. Freeze design changes at a certain point to allow for procurement lead times, approvals etc. When there is a fixed deadline, for example the project under construction has to be occupied at a certain date then a "Point of No More Changes" must be put in place by the contractor. Too often the contractor is held accountable as "the Last Man Standing" - don't be caught in this position. The Contractor Monitor the work done by the earlier contractor or contractors carefully - and make sure delays outside your control are recognized and documented. Delays that are outside your control and impact you financially need to be recorded and the financial impact dealt with by the appropriate responsible person. Remember, you shouldn't bear the cost of other peoples' delays, nor should you be blamed for them! The Workforce Be on the lookout on what your team is doing that may result in delay in delivering the project. Typical examples include starting late, late submission of drawings, mistakes in your drawings. Where the contractor is at fault he has to accept the costs and try and make good the delays and recover the costs incurred. Remember when we are honest about our errors the client will more than readily accept our claims when it's not our fault. Mitigate the impact of the delays by accelerating work and redefine the Critical Path. Whatever the cause of the delay, the contractor must try and recover his position - after all, if a critical date is missed, it may not matter to the client whose fault it is. In case of sub-contracting ensure that the main contractor understands the importance of "Partnering" rather than the usual "Directions" on the project’s progress.In cases where the delays are caused by circumstances beyond the contractors control he should make sure that he is covered financially, typically by means of an extension of time. |
Tuesday, 3 December 2013
Retaining Walls
| Retaining Walls |
| Posted By: Fundi Mjanja on 10th of October 2013 |
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Retaining walls are designed to help
contain soils and hold them in place behind the inside face of a
vertical (wall) structure. They are installed when a large shift in a
site’s grade elevation is desired in a very short distance, in some
cases for aesthetic reasons.
Care must be taken when designing and building a retaining wall since the soils contained behind the wall are trapped at a nearly vertical angle and depending on the height of the wall and the soils there can be tremendous pressures from the soil which the wall must withstand. Additionally, any loads on top of the soil contained behind the wall (known as a surcharge), such as paving or other site improvements, will contribute to an even greater loading on a retaining wall structure. Moisture content and adequate drainage of the retained soils is also an important consideration. Retaining walls can be constructed using different types of materials, and several basic principles may be applied to resist the pressures developed behind the wall. A gravity retaining wall relies on the weight of the wall materials themselves to resist the pressures exerted by the contained soils and surcharge. Rocks and gabions (rock ballast that is usually contained within wire cages) can be employed in a gravity-based retaining wall on principles similar to those of a gravity dam. An example of retaining wall is the cantilever retaining wall. Cantilever retaining wall looks like an inverted letter “T” in cross section. The cross section is designed to adequately contain the soil pressures and any surcharge through its two basic components: a base (horizontal portion) and stem (vertical portion). The outside tip of the base is referred to as the “toe” and the inside tip of the base is the “heel”. A cantilever retaining wall relies much less on material weight, but requires a careful analysis of the loads exerted on the wall components and the soil characteristics at the project site.
Cantilever retaining walls are most often
made of reinforced concrete or combinations of other materials such as
steel and wood. Cantilever retaining wall design must address many
complex forces interacting concurrently; which include the soil pressure
acting on the inside wall stem, any surcharge, soil weights on the wall
base, the soil characteristics beneath the base to resist sliding and
settling and the movements created by all these forces acting at the
heel and toe. Additionally, the connection between the base and stem is a
critical structural detail in cantilever retaining wall design.
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Monday, 2 December 2013
Understanding various Roofing Styles and Slopes 2
| Understanding various Roofing Styles and Slopes 2 |
| Posted By: Fundi Mjanja on 3rd of October 2013 |
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Pyramidal Roof
As the name suggests, this is a type of roof that is shaped like a pyramid.
The pyramid roof is a common variation of
the hip roof, which is known for its gable-less walls which all come up
to meet the roof at the same height. The pyramid hip roof features four
triangular sections which meet at a high point in the center of the
roof, at its peak; the pyramid roof looks very much like a small pyramid
was placed on top of the four walls of the house.
Just like the other types of roofs, the
pyramid hip roof has its advantages and disadvantages. The main
advantage of a pyramid roof is that there are no gables which can offer
significant wind resistance in areas that are prone to extreme wind
conditions. While this makes a pyramid roof sturdier, there is less
space underneath the roof and accessing the inside of the roof to
perform maintenance is somewhat a struggle.
Another positive feature of houses that
have a pyramid roof is that they generally also have eaves around the
four sides of the house and this helps in providing shade to the walls
and can help keep the home cooler during hot weather.
Shed Roof
The shed roof is one of the easiest types
of roof to construct, and for this reason is generally found on smaller
structures that are either homemade or not meant for housing purposes;
hence the name ‘shed’ roof. Generally, if one was to find a shed roof on
a house, it would be as part of an addition. The shed roof is very easy
to spot as it has a single roof face and a single slope. It is commonly
used over a porch or veranda that has been added on to the house.
The construction a shed roof is much easier
as compared to the other roof types and can be done by someone with
basic construction or carpentry skills. The shed roof is relatively
impervious to leaks, which makes it an excellent choice for structures
shed and car parks.
Flat Roof
The flat roof is the most popular type of
roofing and is used on many different home designs as it is one of the
most economical types of roof to construct. A flat roof contains no
slopes, and may or may not have eaves. It is generally made from
materials such metal sheets among others.
Some of the benefits of a flat roof are that it's easier to construct and generally more accessible.
The main downside to this type of roof is
that it requires more maintenance than other roofs because most of the
time debris will collect and settle on the roof. Also a flat roof is
very susceptible to damage from water that collects in the form of pools
or puddles should it should sag anywhere. If this water collects and
retains on the roof for sometimes it weakens the roofing material used
and this may lead to leaking.
In Conclusion
If you are in need of a new roof, and are
unsure about what types and styles will work for your home or building,
consult with a professional in the field. You can get good and qualified
professional for your work by visiting the following link from the
Fundi Mjanja website and contact them directly.
http://fundimjanja.com/index.php?option=com_content&view=article&id=5&Itemid=122
Where you live can make a big difference,
as well as the type of building you are wishing to re-roof. There are
many options available to you and good professionals to assist you in
making this decision.
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Saturday, 30 November 2013
Clerk of works
| Clerk of works |
| Posted By: Blue Print Blog on 7th of November 2013 |
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The Clerk of Works often abbreviated CoW, is employed by the architect or the client on a construction site with the primary responsibility of representing the interests of the client on the project. In addition to recognizing the quality standards of the work the CoW is also charged with ensuring that the quality of both materials and workmanship are in accordance with the design information such as specifications and engineering drawings. The qualification for clerk of works can be held in three specializations: electrical, mechanical and construction. Historically the clerk of works was employed by the architect on behalf of a client or by local authorities to oversee public works. But in modern era the CoW can also be employed by the client (state body/local authority/private client) to monitor design and build projects where the traditional role of the architect is within the design and build project team. The role The role of this position is based on the impartiality of the clerk of works in ensuring that value for money for the client - rather than the contractor - is achieved through rigorous and detailed inspection of materials and workmanship throughout the building process. He should be independent in decisions and judgments. He cannot normally, by virtue of the quality role, be employed by the contractor –but only the client or normally by the architect on behalf of the client. His role is not to judge, but simply to report all occurrences that are relevant to the role. In many cases, the traditional title has been discarded to comply with modern trends, such as site inspector, architectural inspector and quality inspector, but the requirement for the role remains unchanged since the origins of the title. Clerks of works are either on site all the time or make regular visits. They need to be vigilant in their inspections of a large range of technical aspects of the work. The role involves;
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Friday, 29 November 2013
Glass Blocks
| Glass Blocks |
| Posted By: Blue Print Blog on 31st of October 2013 |
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Glass
block is an architectural element made from glass and they are used in a
building to add beauty while at the same time to provide visual
obscuration while admitting light. The glass block was originally
developed in the early 1900s to provide natural light in manufacturing
plants but over the years it has been considered as an element of
interior design commonly applied as part making the interior of the
house more appealing to the eye.
Glass bricks are produced for both wall and
floor applications. Glass blocks for use in floors are normally
manufactured as a single solid piece, or as a hollow glass block with
thicker side walls than the standard wall blocks. These blocks are
normally cast into a reinforced concrete grid-work or set into a metal
frame, allowing multiple units to be combined to span over openings in
basements and roofs. Glass wall blocks should not be used in flooring
applications. Hollow glass wall blocks are manufactured as two separate
hemispheres and, whilst the glass is still molten, the two hemispheres
are pressed together and annealed. The resulting glass blocks will have a
partial vacuum at the hollow centre.
Glass wall blocks in a house are erected after the floor and wall finishes are completed can be erected in short walls of three feet high to full height walls. They can be used to divide an entry porch and a sunken lounge or dinning. The blocks can also be used in a niche that provides light into a dark lobby as well as in the bathrooms as cubicles or for beauty since have they have good aesthetics. When installing glass blocks the area to be walled should be clean and free of any debris and dust and the abutting masonry should have the plaster complete as the blocks will be an in fill as they are not load bearing. The wall can be reinforced on the sides with aluminum frames to house doors or openings. The bonding should be carefully done in accordance to the manufacturer’s instructions. The most commonly used bonding agent with glass wall blocks is Silicon. Care should be taken to ensure that every part of the joint is filled with the adhesive.
When all the courses are complete to the
desired height the top of the wall can be finished with timber, aluminum
or rubber rails. The top finishing is used as a protection for the
glass block and can also be used for holding small flower pots,
portraits, paintings or any other interior beauty enhancing objects.
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Thursday, 28 November 2013
Building a Safe Staircase
| Building a Safe Staircase |
| Posted By: Blue Print Blog on 24th of October 2013 |
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The
staircase in a building is one means whereby one may travel from the
level of one floor to another. The ease with which a stairway can be
traveled depends upon the proper proportioning of the riser and tread of
each step and the number of steps in one series or flight. The design
of the building and the space allowed for stairs will control the type
of staircase which may be built.
The staircase, when carefully designed and built, adds dignity and charm to a home. The quality of craftsmanship displayed reflects the character of the entire interior of the building. In general, stair-work is considered a special field of carpentry. Stairways can be the cause of the greatest number of accidents in the home. These accidents can be attributed to various factors; some, of course, are beyond the control of those who design and build the stairways. However, there are far too many accidents due directly to faulty construction. The carpenter can make a worthwhile contribution toward accident prevention if he plans and does his work well. The following standards and suggestions should be observed when building the staircase to help avoid some of the causes responsible for the accidents;
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Wednesday, 27 November 2013
The Collapse of Buildings
| The Collapse of Buildings |
| Posted By: Blue Print Blog on 17th of October 2013 |
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Buildings, like all structures are designed
with special attention to allow the support certain loads without
deforming. The loads that are taken into account during the design stage
of any building include both live loads and dead loads like furniture
and equipment. For a building to be declared safe for occupation it must
be able to withstand the weight of rain and the pressure of wind as
well as bear the load of the building itself.
Buildings that comprise fewer floors, strength generally accompanies sufficient rigidity and the design is mainly that of a roof that will keep the weather out while spanning large open spaces. With tall buildings that consists of several floors the roof becomes a minor matter and the support of the weight of the building itself should be the main consideration since just like long bridges, tall buildings are subject to catastrophic collapse if considerable care is not taken during the design stage.
The main causes of collapse in buildings can be generally classified under the following;
Bad Design Bad design due to errors of computation and failure to take into account the loads the structure will be called upon to carry, erroneous theories, reliance on inaccurate data, ignorance of the effects of repeated or impulsive stresses, and improper choice of materials or misunderstanding of their properties may easily result into a collapse of the building. The engineer should take a keen interest during the design stage as he is bound to be held responsible in the event of these failures. Faulty construction Faulty construction has been the most often cause in recurrence of structural failure. This may occur due to mistakes arising from lax in inspection which includes the use of salty sand during concrete mixing, the substitution of inferior steel for that specified, bad riveting or even improper tightening of nuts, bad welds, and other practices well known to the construction worker. Foundation Failure Even an excellently designed and constructed structure will not stand on a bad foundation. Although the structure will carry its loads, the earth beneath it may not. The Leaning Tower of Pisa is a famous example of bad foundations but it is not the only one. The old armory in St. Paul, Minnesota, sank 20 feet or more into soft clay, but did not collapse. The displacements due to bad foundations may alter the stress distribution upon the building significantly. Extraordinary Loads Extraordinary loads are often natural, such as repeated heavy snowfalls, or the shaking of an earthquake, or the winds of a hurricane. A building that is intended to stand for some years should be able to meet the challenges of extraordinary load that may arise from frequent earthquakes and strong winds. Even a solid masonry building would be destroyed in an event of earthquakes if the foundation is not designed carefully to withstand external natural strains. |
Tuesday, 26 November 2013
Building Demolitions
| Building Demolitions |
| Posted By: Blue Print Blog on 3rd of October 2013 |
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Demolition projects can range from small,
simple jobs to complicated undertakings that require sophisticated and
detailed planning. Site conditions can vary significantly, and there is
always a degree of imprecision to the wrecking of the building itself.
For typical building demolition and site improvements the most common
procedure is to use heavy mechanical equipment such as wrecking balls,
excavation hoes, grapples, crushers, and hydraulic breakers and shears.
Several factors need to be considered prior to and during demolition,
including the scheduling of demolition activities, protecting the site
(especially important with occupied structures), and dealing with
hazardous materials.
With the demolition of structures, the owner, architect, engineer and demolition contractor need to be aware of the regulations that govern the demolition of buildings. Prior to allowing the demolition squad to start demolition operations, an engineering survey of the building that is marked up for demolition should be carried out by a competent and qualified person to determine the condition of the framing, floors, and walls, and possibility of unplanned collapse of any portion of the building. The demolition team should have in writing evidence that such a survey has been undertaken and the demolition process has been given a go ahead from the relevant authorities. Building demolition can include items that may not be apparent at first such as any below-grade structures that would include various types of footings and foundations. Also underground utilities that provided services to the building and the adjacent buildings will need to be considered during demolition. In rural areas--where buildings are not densely packed--and the built structures themselves are often smaller with fewer recyclable materials, demolition is usually uncomplicated, in that the structure can be knocked down and the debris can be removed all together but in urban and densely packed areas, demolition projects may require the hiring of an architect or engineer to produce documents, drawings, and specifications for building demolition. Contractors who specialize in demolition need to come up with a demolition schedule to manage the project. If the owner will be occupying a portion of the site or building during demolition, a schedule of demolition activities will be useful to avoid interference with any concurrent operations and to minimize any disruption of utilities and services. The owner may have additional restrictions that the contractor will need to consider when scheduling activities. Some typical owner restrictions include the protection of exterior stairs, loading docks, and entries of adjacent buildings, as well as a limitation on hours during which demolition operations may take place. However, every additional restriction the contractor needs to manage will usually be reflected in higher demolition costs. In areas with greater population density, the demolition of structures is not necessarily more complicated.
Some situations are complex and mandate a
high level of sensitivity to how demolition is handled, for example,
demolition that takes place on a hospital campus. In these instances, a
careful, piece-by-piece dismantling of the building is usually
necessary, with material sorting often taking place on site. For such
projects, an engineer or architect will need to be consulted to produce
specifications to which the demolition must conform. The architect or
engineer will produce the necessary documents which clearly outline the
requirements for protecting individuals, adjacent buildings, and any
remaining site improvements and utilities during the demolition
operations.
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Monday, 25 November 2013
Quality Construction of Suspended Floors
| Quality Construction of Suspended Floors |
| Posted By: Nyumba Imara Blog on 7th of November 2013 |
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Building suspended floors that are
acceptably flat and level is one of the many challenges that contractors
may have to face in the course of a project construction. Whether
supported by steel beams or a cast-in-place concrete frame every
elevated floor deflects or sags slightly under its own weight.
Structural drawings generally require that individual floor framing
members have a slight camber, or hump in their profile prior to
construction so as when cambered floor framing members are allowed to
deflect they ideally will move to a level position. When everything
works right, the floor’s finished surface will then perfectly complement
structural deflection.
Forms and shoring should be designed to allow safe, easy removal, while protecting the structure from excessive deflections at early stages. However buildings come in many shapes and sizes and as the available materials and floor framing are assembled together unique combinations are created thus the resulting floor systems do not always deflect to the engineer’s expectations. That's why the successful contractor must remain flexible and be ready to respond to jobsite developments. Success depends on two things—an effective preconstruction planning program and the ability to identify and adjust to unexpected conditions. Monitoring the Construction The goal in constructing any project is to meet and if possible exceed the requirements of the specifications. When evaluating construction of floors, the following standards, depending on the structural system should apply;
The following are essential elements to be put in place so as to achieve a quality suspended floor;
Controlling quality Controlling the elevation of the supporting platform requires that engineering controls be established. The monitoring program for a structural steel frame provides key information about critical components such as base plate, column splice, and beam-to-column connection elevations, along with deflection of typical framing members. On a cast-in-place concrete frame, the contractor should select forming and shoring systems. Forms and shoring should be designed to allow safe, easy removal, while protecting the structure from excessive deflection at early stages. Evaluating concrete mix designs, delivery systems, and finishing techniques provides an opportunity to achieve the quality standards. Each decision will impact the flatness and levelness of the finished floor. Concrete mixes must develop adequate strength while providing good consolidation, consistent set time, and workability. The workers involved on the project must be capable of producing work that conforms to the quality standards. Concrete finishing techniques must produce the desired results. The pre-construction meeting is a good opportunity to address the team's plan for coping with isolated locations where actual deflection of the floor might be different from what is expected. Discussing job site controls for structural steel, form-work, reinforcing steel, concrete, and finished surface profiles will help ensure that backup systems are ready. Changes and substitutions in materials or admixtures should not be made without notifying and obtaining approval by the rest of the design/construction team. |
Saturday, 23 November 2013
Common Plaster Problems
| Common Plaster Problems |
| Posted By: Nyumba Imara Blog on 31st of October 2013 |
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When
plaster dries, it is a relatively rigid material which should last
almost indefinitely. However at times the plaster work may start
cracking due to several conditions. Some of the conditions that may
cause the plaster to crack, efflorescence (that is to lose moisture and
turn to a fine powder on exposure to air), separate, or become detached
from its lath framework include;
• Structural problems • Poor workmanship • Improper curing • Moisture Structural Problems
1. Overloading
Stresses within a wall, or acting on the house as a whole may end up creating stress cracks. Appearing as diagonal lines in a wall, stress cracks usually start at a door or window frame, but they can appear anywhere in the wall, with seemingly random starting points. The weight of the roof, the second and third stories, the furniture, and the occupants may impose a heavy burden on beams, joists, and studs. Even when houses are built properly, later remodeling efforts may cut in a doorway or window without adding a structural beam or "header" across the top of the opening. Occasionally, load-bearing members are simply too small to carry the loads above them and may lead to deflection or wood "creep" (deflection that occurs over time) thus creating cracks in plaster. Overloading and structural movement combined with rotting floorboard, rusted nails, or poor quality plaster results in the plaster detaching from the lath (floorboard) therefore losing its key. When the mechanical bond with the lath is broken, plaster becomes loose or bowed and if repairs are not made, especially to ceilings, gravity will simply cause chunks of plaster to fall to the floor. 2. Settlement/Vibration Cracks in walls can also result when there is settlement in a house. Houses built on clay or black cotton soils are especially vulnerable to cracks when settlement occurs as clay soils are highly expansive. In the dry season, water evaporates from the clay particles, causing them to contract. During the rainy season, the clay swells thus causing a building that is not structurally sound to be riding on an unstable footing. Diagonal cracks running in opposite directions suggest that house settling and soil conditions may be at fault. Similar symptoms occur when there is a nearby source of vibration-blasting or busy highway. 3. Lath Movement Horizontal cracks are often caused by lath movement. Because it absorbs moisture from the air, wood lath expands and contracts as humidity rises and falls. This can cause cracks to appear year after year. Cracks can also appear between rock lath panels. A nail holding the edge of a piece of lath may rust or loosen, or structural movement in the wood framing behind the lath may cause a seam to open. Heavy loads in a storage area above a rock-lath ceiling can also cause ceiling cracks. Errors in initial building construction such as improper bracing, poor corner construction, faulty framing of doors and windows, and undersized beams and floor joists eventually manifest through to the plaster surface. |
Friday, 22 November 2013
Testing Drainage Pipes After Laying
| Testing Drainage Pipes After Laying |
| Posted By: Nyumba Imara Blog on 24th of October 2013 |
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| Drains must not be covered over until they have been inspected and tested for leaks and the the joint performance.
Two tests, a roughing test and a final
test, should be applied to the drainage system in every building. The
roughing test may consist of a water test or an air test, The water test
is the one most commonly used, and during warm weather is the most
convenient test to apply. It cannot, however, be applied conveniently in
cold climates.
The water test is applied by closing all openings to the drainage system, except those above the roof, and filling the system with water until it overflows the vent stacks. It is a more severe test than an air test and also a more unevenly distributed one. To apply a roughing test it is necessary to close all openings to the system. Lead closet bends, and all lead pipes or traps that project from floors or walls should be closed by soldering a round disk of sheet lead over the opening. This should be done at the time of installing the lead work to prevent anything entering the drainage system and also to preserve the shape of the outlets for the walls and floors to be fitted to. Openings to wrought-iron drainage systems and wrought-iron vent pipes can be closed by means of screw plugs or capped nipples. When necessary to extend an outlet from behind a wall or partition, a capped nipple should be used. To close openings in cast-iron pipe, special plugs or stoppers must be used as they can be easily removed without jarring the pipe after the system is tested. A Testing Plug that is used for closing openings to cast-iron pip is held in place and made water tight by a rubber band under compression bearing against the inner surface of a pipe or fitting. The testing plug should be placed inside of the spigot end a of pipe or fitting and not in the hub, as the increased surface exposed to the pressure of water or air when placed in a hub increases the liability of the plug blowing out. These plugs are only suitable for testing systems where the head of water does not exceed 50 feet. Where plugs of this type are used, a stop cock c can be substituted for the cap on the end of the handle, and the system can be filled and emptied through the stop cock. When testing the drainage use the type of stopper that cannot be blown off under any pressure likely to be encountered in testing drainage systems. When applied to the spigot end of a pipe the stopper must be provided with a collar to hold the clamps. Stop cocks can be screwed to the capped outlets of these soil pipe plugs through which to fill and empty the system. |
Thursday, 21 November 2013
Laying Drainage System Pipes
| Laying Drainage System Pipes |
| Posted By: Nyumba Imara Blog on 17th of October 2013 |
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Drainage systems are a common encounter our
everyday world of building and construction. Most often people think of
drainage as a piping systems of underground structures used to convey
liquids of one sort or another. To a layman, the concept of drainage
system installation sounds as easy and straight forward as digging a
trench, laying the pipe in the trench and filling covering the trench.
Inasmuch as this simplified perspective of pipeline construction may be appealing, it does not to address the engineering concepts that must be observed in any drainage system and the underground installation of a pipeline. Generally there are two objectives that must be achieved in any drainage system installation. The first is to provide an envelope of embedment to protect the pipe from mechanical damage that may be caused by impact or hard objects like cobbles and boulders in the soil and is second is to cushion and support the pipe against earth and live load pressures. Some pipes are designed carry more loads and require less support from the soil but when support is needed to protect the pipe embedment should be applied around the drainage pipes. The embedment material used must be well compacted so as to provide sufficient resistance to the weight that earth and live loads may impose on the pipes. The trench back-fill placed on top of the embedment material should also be compacted as compaction of trench back-fill immediately above the pipe facilitates the redistribution of some of the load away from the pipe and into the side-fill soil. Let’s now take a look at what the laying of a drainage system involves; Foundation In some soil condition it may be found that the trench bottom cannot provide a firm working platform for placement of the pipe bedding material. In such conditions foundation is required to provide a solid base on which the drainage pipes may rest undisturbed so as to maintain a constant flow of the liquids being conveyed through it. The pipe’s ability to support loads and resist deflection is determined by the quality of the embedment material and the quality of its placement. Laying of drainage foundation in the initial back-fill zone includes bedding, haunching, primary, and secondary zones. Bedding Bedding plays a crucial role in leveling out any irregularities and ensures uniform support along the length of the pipe. It also helps bringing the trench bottom to required grade. Haunching Hauching refers to back-fill under the lower half of the pipe. It helps in the distribution of the superimposed loadings. The nature of the haunching material and the quality of its placement are one of the most important factors in limiting the deformation of the drainage pipes. Primary Initial Back-fill This zone of back-fill provides the primary support against lateral pipe deformation. To ensure such support is available, this zone should extend from trench grade up to at least 75 percent of the pipe diameter. Under some conditions, such as when the pipe will be permanently below the ground water table, the primary initial back-fill should extend to at least 6 inches over the pipe.
Secondary Initial Back-fill
Secondary initial back-filling helps in the distribution of overhead loads and isolate the pipe from any adverse effects of the placement of the final back-fill. Final Back-fill Since the final back-fill is not an embedment material, its nature and quality of compaction has a lesser effect on the flexible pipe. However, arching and thus a load reduction on the pipe is promoted by a stiff back-fill. To avoid the possibility of impact or concentrated loadings on the pipe both during and after back-filling, the final back-fill should be free of large rocks, organic material and debris. The material and compaction requirements for the final back-fill should reflect sound construction practices and satisfy local ordinances and sidewalk, road building, or other applicable regulations. |
Wednesday, 20 November 2013
Choosing Paint Colors for Different Rooms
| Choosing Paint Colors for Different Rooms |
| Posted By: Designer Mjanja Blog on 7th of November 2013 |
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Paint color is widely known to have quite a
considerable effect on many elements in a room’s design scheme. The
color applied on the walls, trim and ceiling can affect the atmosphere
and mood while also reflecting the overall design style. Paint color can
be used to highlight or emphasize architectural features or downplay
them when you want a different effect. Having these factors on mind can
help you choose the best colors even in challenging rooms with unusual
design features such as living rooms with lofts.
Room Size Emphasis The design of a high ceiling living room with is similar to that of a great room. If you choose to emphasize this design feature, paint the room in very light colors such as shades of white or beige. White colors with cool undertones of blue or green will make the walls and ceiling appear to recede thus emphasizing the spaciousness. Pale shades of blue or green will have the same effect. White colors with warmer undertones of yellow or pink will lessen the effect slightly. Room Size Downplay If you aim to lessen the effect of a large space and create more of a warm, enclosed space, choose a darker and warmer color. Muted hues in golden yellow, orange or red will make the walls appear to advance. Dark brown will warm the room and make it appear smaller. Dark blue or green can make the room feel hollow. When aiming to downplay the room size care must be taken when it comes to choice of the color to apply as a dark wall color is harder to change should you decide that the color doesn’t look appealing anymore. If you use a darker color and decide to change it to a lighter one you will first have to cover the dark color with primer before painting the walls a lighter color. Try on a dark color by painting just one wall and observe the color effect under different lighting. If the color appears to be overwhelming on all the walls, keep the painted wall as an accent wall and choose a lighter shade in the same tone or a coordinating tone for the rest of the walls. Design Style Consider choosing the paint color that will enhance the design and style of the building. Most often go for bold and brighter colors when dealing with modern styles of architecture. For traditional home styles go for deep or dark color as they add some sense of sophistication to the home. Coastal, beach or cottage-style homes are often painted in light or pastel colors. Rustic and country homes tend to embrace natural colors with an emphasis on nature. Neutral color schemes are commonly found in contemporary homes and are quite satisfying to the sight when blended with accents rich in color and texture. |
Tuesday, 19 November 2013
Interior Lighting Part 2
| Interior Lighting Part 2 |
| Posted By: Designer Mjanja Blog on 31st of October 2013 |
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In
this article we continue highlighting the common lighting mistakes to
avoid and give some tips on how get you house lighting right;
Using incandescent or halogen sources without dimming While it is common for us to find ways of retrofitting lighting with more efficient, longer lived light sources than incandescent we should not forget that this type of lighting is still a viable and important part of lighting in a residence, provided it is dimmable. By dimming, we decrease energy and heat output, and we lengthen lamp life. Non- incorporation of Ambient, Task and Accent Lighting
Lighting designers understand that all
well-designed spaces incorporate different types of light. Ambient light
is general lighting for walking around, conversing, and identifying
objects. Task lighting provides higher, more concentrated lighting for
tasks such as chopping vegetables, shaving, or reading. Accent light is
used to highlight artwork or architectural features, such as the
beautiful glass tile you’ve specified in the bath or the ceramic
collection your client will showcase in open shelves in the kitchen.
Combining all three types of light gives greater functionality,
interest, and likelihood that you will have sufficient lighting.
Neglecting to control different types of light separately
For maximum efficiency and flexibility,
each type of light should be controlled separately and any incandescent
or halogen light or dimmable LED's should be dimmed. Controlling
multiple sources can be achieved by the old school method of multiple
light switches, but there are many more sophisticated ways to achieve
control. From a simple programmable wall box system for single room
control with preset scenes, to wireless controls that generate their own
power and can be reprogrammed from a laptop. Controlling the lighting
yields energy savings combined with the right amount and type of light
for different times and uses.
High Ceiling Recessed Down lights for Ambient light
This results in a lot of wasted light and a
very dark space. Light originating at high ceilings needs to have a
focused tight beam spread with enough center beam candle power, such as
that from a ceramic metal halide or high wattage halogen source. Better
yet, using wall-mounted or pendant sources to reflect light off a
ceiling surface often provides much better illumination than punching a
lot of holes for recessed down lights.
Decorating with light Decorating with light fixtures, or choosing fixtures based on how they look rather than their light output, performance and distribution often results in a waste of energy and less than optimal light output. For assistance with architectural light fixture choices, consider hiring a professional lighting designer who can transform your space through light, while providing adequate task lighting and often saving energy.
On the Fundi Mjanja website, such professionals are listed under Interior Designers and can be found on the following link;
http://www.fundimjanja.com/index.php?option=com_category&view=components&Itemid=122&cartId=33
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Monday, 18 November 2013
Interior Lighting part 1
| Interior Lighting |
| Posted By: Designer Mjanja Blog on 24th of October 2013 |
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Interior designers are often called upon to
give input about lighting in residential environments. In trying to
tackle a lighting dilemma, many fixtures get specified in living areas,
kitchens and baths that waste energy and do not get light where it is
needed most. These ineffective specifications are often repeated as
homeowners are unsure of lighting solutions and tricks of the trade.
Sometimes knowing what to do can help make you look like a pro.
This article highlights the common lighting mistakes to avoid and gives some tips on how to do it right. Over doing Recessed Down lights This is one of the most common errors that lighting design professionals see. Builder spec versions of can lights are quite affordable and people often assume that laying them out in a regular grid gets light everywhere. Unfortunately, this is not so. The optics of inexpensive can lights often allow only slightly more than half the lumen output of the lamp to escape. In addition, can lights, unless they are adjustable or wall wash fixtures, typically don't put sufficient light on vertical surfaces, which is where the eye perceives light. With an array of cans, we might waste nearly half our watts and still have a space that feels like a cave because the walls are dark. Kitchen Task lights There are many better ways to light the counter, and one of them is to use fluorescent or LED task lights under the upper cabinets. If your kitchen design lacks upper cabinets over some work surfaces, don't worry. This is a situation where wall-mounted or ceiling recessed adjustable fixtures with the right lamp make all the difference. Adding several low voltage halogen fixtures with a narrow flood beam distribution and focusing them on the task area will do the trick. Remember to choose your fluorescent or LED color temperature wisely. Down lights without Side lights Standing directly under a down light, without any light at the sides of the face, creates exaggerated and unflattering shadows. In the bathroom, using a down light over the sink is fine to accent the expensive polished nickel faucet you've specified, but it is insufficient for tasks like shaving, tweezing, and applying makeup. For this, we need light at the sides of the mirror at eye level to minimize shadows and provide even distribution. This can be achieved with sconces flanking the mirror. |
Saturday, 16 November 2013
Reducing Weight in Suspended Concrete Floors using Hollow Blocks
| Reducing Weight in Suspended Concrete Floors using Hollow Blocks |
| Posted By: Fundi Mfalme Blog on 10th of October 2013 |
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Suspended concrete floors are found in
storeyed buildings. The self-weight of concrete without additional live
loads is great but buildings where the spans are large, weight reduction
is done to avoid buckling of the floor. Buckling is where the concrete
sags at the middle.
The concrete is laid the same way but
hollow blocks are added to reduce weight. The blocks are hollow in the
middle and the reinforcements are laid in between them then concrete is
added and vibrated to hold them together.The top concrete is about
seventy six millimeters (three inch) thick.
The suspended concrete floor hollow blocks are either clay or concrete blocks. The blocks are two hundred to two hundred and fifty millimeters thick. The blocks that are at the beginning and at the end of a row are blocked on one side to avoid concrete from flowing inside the blocks.
The ceilings from this kind of floors are
flat and the ordinary down stand beams are not visible from below the
slab soffits making these kind of floors ideal over big rooms like
lounges, dinning and offices.
When the suspended slab form work is ready, the laying of the hollow blocks commences. The external beams are then laid into the forms. The internal beams for this kind of floors are laid within the slab thickness. These beams will span from the external ones across the room to the other end. The beams are also laid where walls are to be built on the slab. The hollow blocks are then laid on the form work in between the beams. They are arranged in rows of nine hundred millimeters wide with a spacing of a hundred millimeters after every nine hundred millimeters (blocks) row. Once the hollow blocks are laid, the gaps in between are fitted with reinforcements. This bars span from the end beams and they are to hold the concrete together. A mesh fabric is then laid on top of the hollow blocks. After this is done concreting work commences. The concrete should be well vibrated to ensure the blocks are held tightly together. The concreting is done normally and is leveled and made smooth. Curing is done for twenty one days before stripping off the formwork to pave way for plaster finishes. |
Friday, 15 November 2013
Clay Tile Roof Repair
| Clay Tile Roof Repair |
| Posted By: Fundi Mfalme Blog on 17th of October 2013 |
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A
clay tile roof is often susceptible to leaks caused by various problems
either with the tile itself or by the method of installation hence the
method employed in the repair of a leak will often differ depending on
the cause of the problem.
More than any other roof type, the
traditional tile roof is an architectural feature deserving of special
attention because the texture, color, and play of light and shadow
impart a distinctive character to a building that no other roof type can
match. Yet tens of thousands of tile roofs have been lost in recent
decades because of the ignorance or laziness of low-level roof repair
contractors. So it is of paramount importance to have your tile roof
fixed by a qualified and experienced roofer.
Leaking in clay roof tiles may be due to several faults. Some leakage problems go beyond the roof clay tile being related to the other aspects of the roofing or installation methods. Some of the common problems that relate to leakage in clay tiles are:
The defects that may result in a leaking clay tile roof can be dealt by a careful consideration of the following measures; Fixing a Membrane More than often the leakage may be as result of defective in the waterproof membrane. If such is the cause of the leakage then the waterproof membrane will need to be replaced. This is done by removing all the existing tiles and replacing the old membrane with a new one. Then the roof is re-tiled. This must be done by the help of a professional to avoid a re-occurrence of a similar problem in future. Removing the Debris It is a common occurrence for the roof valleys especially the closed ones to collect a lot of debris. More often than not, this can cause leaks in clay roof tiles. In order to remove the debris such that there is no more leakage, you will need to remove the tiles from the valley, clean out the area, and then reinstall the tile. You may also need to consider converting the closed roof valleys into open ones to avoid debris collection in the future.
Fixing a Crack
If you find that there are fine cracks in your tiles, you can repair the crack by applying a crack sealant to the tile to deal with the problem. When applying the crack sealant allow it to spread over the entire tile and let it dry. Fixing Broken Tiles Tiles that are broken or have large cracks need to be replaced in order to fix the leak. For this, you will need to remove all damaged tiles. The removal must be carefully done to avoid causing damage to the good tiles next to the broken ones. If your roof is old, chances are your tiles have been fixed using mortar. If that is the case, place the new tiles and use the mortar to seal them in place. Metal Flashing In some cases the leakage in the roof might be as a result of failure of metal flashing. If the metal flashing is the source of the leakage then it's possible to lift a limited number of tiles, replace all flashing and re-lay the original tiles. During this process, you may also find some broken or cracked tiles. (An experienced roofer can tell by gentle tapping whether a tile retains its structural integrity or has hidden fissures.) Cracked or leaking tiles should be replaced at this time.
Work on an existing tile roof must be done
by an experienced roof tile contractor; an inexperienced contractor may
break more tiles than he or she replaces.
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Thursday, 14 November 2013
Fixing a Tile Roof Underlay
| Fixing a Tile Roof Underlay |
| Posted By: Fundi Mfalme Blog on 24th of October 2013 |
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Roofing underlays are used underneath the
final tile roof covers. They are fixed before laying roofing tiles or
shingles so as to prevent any rain water from passing through to the
ceiling as the tiles or shingle roof covers may allow water to seep
through when broken. Roofing underlays can be polythene or bituminous
in nature or as it is common nowadays plain metal sheets or corrugated
iron sheets. The placing of the felt or underlay should be done by a
qualified carpenter and with due diligence as this will help to
safeguard the ceiling and entire house from any roof leaks. For the
roofing felt to function effectively care must be taken when laying it
to ensure that it is free from any punctures as these are likely points
that water may pass through to the ceiling of the house.
When using polythene, it should be heavy gauge and preferably laid in two sheets. This is because the temperature in the roof space may rise thus leading to damages on the felt. The bituminous felt should preferably be the sand blasted type. This is able to take higher temperatures without breaking within the roof space. The felts should be laid smooth from the ridge to the eaves. This prevent them breaking after they become brittle during the cold season. Metal iron sheet has become the most preferred roof underlay in the recent years as it is more durable and reliable. In comparison to polythene underlays it is less susceptible to damage during installation thus preventing the likelihood of any leakages after installation. It is durable, wind- and fire-resistant and practically maintenance-free, but it must be installed properly by a qualified metal roof carpenter as its installation requires specialized skills. However, the options and installation process for metal underlay are largely the same as shingles or other roofing materials. When laying polythene roofing felt, ensure the surface is horizontal and level. The roof structure is first completed then polythene is laid using plastic straps. The straps are nailed on the purlins in a mesh pattern and they should be tight to prevent sagging under water weight. After completion the polythene underlay is laid on top then the roof battens are nailed onto the purlins according to the tile specifications. The laying of tiles is then done after testing for sagging or any leaks within the felt. |
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