Importance of Steel Reinforcement in Concrete Slab 2

Importance of Steel Reinforcement in Concrete Slab 2

Posted By: Fundi Mjanja on 7th of November 2013

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: Steel reinforcing is simple to place Steel reinforcing reduces random cracking Steel reinforcing reduces and controls crack width and helps maintain aggregate interlock Displacement and curling can be minimized when steel reinforced concrete is used Strength is increased with steel reinforced concrete—even the smallest cross sectional area of steel reinforcement will provide considerable reserve strength 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.

Importance of Steel Reinforcement in Concrete Slab

Importance of Steel Reinforcement in Concrete Slab

Posted By: Fundi Mjanja on 31st of October 2013

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.

Constructing on a sloppy Terrain

Constructing on a sloppy Terrain

Posted By: Fundi Mjanja on 24th of October 2013

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.

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

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. Delays on the client part may arise because of change of mind regarding what he aspires to achieve on his project, communicating their instructions too late or dragging their feet when it comes to approving changes on the project, etc. They tend to overlook the fact that the delays on their part push ahead the finish date of the project and this renders the contractor powerless to avoid delay in delivery of the project. Delays by the main contractor may result through mismanagement and lack of proper coordination. Last but not least, contractor may himself cause delays, for example by under-resourcing the project in the early stages or not completing design drawings and getting them approved in time. 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.

Retaining Walls

Retaining Walls

Posted By: Fundi Mjanja on 10th of October 2013

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.

Understanding various Roofing Styles and Slopes 2

Understanding various Roofing Styles and Slopes 2

Posted By: Fundi Mjanja on 3rd of October 2013

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.