Building a Safe Staircase

Building a Safe Staircase

Posted By: Blue Print Blog on 24th of October 2013

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; Stairways should be free from winder The dimensions of landings should be equal to or greater than the width of stairways between handrails (or handrail and wall) Landings should be level and free from intermediate steps between the main up flight and the main down flight. All treads should be equal and all risers should be equal in any one flight. The sum of one tread and one riser, exclusive of the nosing, should not be more than 18 inches nor less than 17 inches. (Stair ratio). The nosing should not exceed 13/4 inches. All stairways should be equipped with permanent and substantial handrails 36 inches in height from the center of the tread. All handrails should have rounded corners and a surface that is smooth and free from splinters. The angle of the stairways with the horizontal should not be more than fifty degrees nor less than twenty degrees. Stair treads should be slip proof, firmly secured and with no protruding bolts, screws, or nails.

The Collapse of Buildings

The Collapse of Buildings

Posted By: Blue Print Blog on 17th of October 2013

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 Faulty Construction Foundation Failure Extraordinary Loads 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.

Building Demolitions

Building Demolitions

Posted By: Blue Print Blog on 3rd of October 2013

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.

Quality Construction of Suspended Floors

Quality Construction of Suspended Floors

Posted By: Nyumba Imara Blog on 7th of November 2013

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; Structural steel must be properly erected Steel connections must conform to the contract document requirements Concrete reinforcement must be placed and maintained in the proper location Concrete mix design, strength, and slump must conform to the specification Finished floor surfaces must meet the specified tolerances for levelness and flatness. The following are essential elements to be put in place so as to achieve a quality suspended floor; Preconstruction planning and meetings to minimize potential problems Gathering information during construction to allow evaluation of the work Responding to unexpected results by adjusting the design or construction Confirming that the adjustments are successful. 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.

Common Plaster Problems

Common Plaster Problems

Posted By: Nyumba Imara Blog on 31st of October 2013

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.

Testing Drainage Pipes After Laying

Testing Drainage Pipes After Laying

Posted By: Nyumba Imara Blog on 24th of October 2013

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.

Laying Drainage System Pipes

Laying Drainage System Pipes

Posted By: Nyumba Imara Blog on 17th of October 2013

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.