Steel Building Construction Considerations

One of the first prerequisites before actual construction begins is the thorough inspection of the conditions of the proposed building site. This is usually done well in advance of the final planning stage since site conditions affect the total costs that are to be included in the proposal.

Site Considerations


Building Codes

Most cities and towns of any size have instituted building codes that protect the public against injury to life and property. The types of construction, quality of materials, floor loads, allowable stresses and many other requirements relating to buildings are covered by these codes. A building department or a local building official generally administers codes, which examines and approves plans of proposed buildings. These officials will visit buildings during construction to make sure the buildings are being constructed according to the drawings the officials or the building department previously approved.

Codes vary widely in their requirements, from city to city, and county to county. It is important to become familiar with the various codes and regulations enforced in your specific market area.

Zones

Zoning should always be considered before the site selection is final.

Zoning ordinances regulate the size and use of buildings and the use of land. Four types of zones are generally recognized throughout a city:

  • Residential
  • Business
  • Industrial
  • Unrestricted

Business zones are areas incorporated within reasonable walking distances of residential areas for marketing and shopping. Industrial zones are areas generally near waterways, railroads and other transportation connections for manufacturing and commercial use. Outlying districts are zoned in the same manner to maintain them for present or future use. Each city or county has different zoning laws; therefore, it is essential to become familiar with the zoning laws in your specific market area.

Restrictions

Restrictions of a building site (as defined by codes and zones) must be considered before final plans of a building are completed, since they can affect the size and type of structure. Examples of typical restrictions may be:

  • Buildings, as a rule, are not permitted to cover the entire lot. Uncovered spaces, such as courts, yards, etc., must be provided so that light and air are available to the occupants. This, of course, limits the square footage of possible floor space.

  • Buildings also are restricted as to permissible height. Depending on the zone, taller buildings can be erected if portions of a building are set back a certain distance from the street.

  • Off-street parking requirements are another frequent restriction.

  • Availability of access to the building site can often be a safety restriction. The site might be located adjacent to a proposed interstate-highway system which, when built, would limit convenient access to the property.

Building restrictions vary considerably from one community to another. You will need to confirm your location is Zoned or approved appropriately.

Utilities

One of the first steps in the preparation of the site is consideration of the utility connections: water main, sewer, gas main, telephone, and electrical service lines. Water, sewer, and gas mains are generally located in easements parallel to property lines or adjacent streets. Occasionally, they are located beneath streets or on the other side of the street from the site that require boring or tunneling for access.

Permits are often required to connect to the main sewer line, water, and gas line. Inspections are required, and in some cases, "tap" fees are charged to connect.

Telephone and electrical lines provide more convenient connections since they are usually exposed above the ground. However, more and more telephone and electrical cables are being installed underground as well. Some zones even require all cables to be buried. Excavation should never be attempted without notifying the local utility coordinating group to verify existing utility locations.

Electrical subcontractors take care of all necessary wiring, but they do not make connections to the main line. This is performed by the local power and light company, which inspects the electrical work before making the final hook up. In most metropolitan areas, electrical work is also subject to inspection by the local building official or department.

The telephone company usually handles telephone connections. You will need to consider conduits within the floor or wall system.

The exact location of service lines should always be considered, since utility companies charge on the basis of "distance from the nearest source" (power line, water main, and so on) to the buildings. This, of course, affects the total cost of the project.

Soil

It is essential to know the soil's characteristics before building construction begins. Is it hard or soft? Is the soil composed of rock, boulders, gravel, sand, or clay? What are the specific sizes of the composition? Open test pits, loading box and platform, and test borings are three types of soil tests used to determine soil composition. These tests establish the bearing value of the soil, which in turn determines the amount of weight the soil will support.

Firms specializing in this service, such as testing laboratories, normally perform testing.

It is not necessary that you know how to perform these tests, but you should become familiar with soil conditions in your area, and realize their importance to the total project. Many cities have established presumptive bearing capacities, which determine the maximum allowable loads that are placed on building sites. Soil tests are usually performed prior to foundation and paving design.

Site Preparation

Prior to the actual construction of the building, the first step is the preparation of the site. The land is surveyed to establish the exact boundary of the plot. In this survey, the building is also located and the desired grade level is staked out.

The exact elevation of the building, and the grade level, are established by the use of a surveyor's instrument called a level. The elevations are usually set in relation to the top of the road or nearby buildings.

The land is then cleared of all obstructions, such as trees or boulders, which interfere with the construction project. If it is necessary to remove any existing buildings, a wrecking or demolition contractor performs this work prior to the rough grading or rough leveling of the land.

Grading

Rough grading is leveling the site to conform to the designed building and site elevations. This is usually called the subgrade. The rich top layer is removed and saved to be spread over the area later.

After the site has been leveled, the exact location of the building is marked. With the use of a transit and a measuring tape, the corners are located and staked out according to the plans.

Excavation and Fill

Excavation is digging out or hollowing the land to prepare it for the necessary footings and foundations of the structure. There are two general types of excavation performed on most construction projects:

  1. General excavation - The bulk of the earth and rock is removed to prepare for the footings and foundation walls of the structure. An amount sufficient for back filling and final grading should be retained.

  2. Minor excavation - Pick and shovel are used for trimming up trenches and footings prior to the actual pouring of concrete. In some cases small machines may be utilized to handle minor excavation work.

Fill or back fill might also be required in order to achieve the necessary grade level. Filling is simply adding earth and rocks where void places exist. In cases where the slope of the land is abrupt, it may be necessary to build walls to support this fill. When back filling the soil must be well compacted or packed solidly in order to insure against future settlement.

Drainage

Throughout the site preparation, excavations should be kept dry. Whenever ground water is present, it should be removed from the site, either by draining into prepared pits, or by pumping out the water. Some site locations might even require the placement of well points, where pipes are put into the ground to drain water from various locations. However, regulations should be checked before any drainage system is installed. This should be a part of any good site plan. A lot of foresight is necessary in considering drainage systems. It might prevent future problems and extra expense.

Concrete Work

Concrete Work Photo

Concrete presents a substantial part of most building projects, regardless of the size. Like almost any other material, it can give good service for years, or be a source of real problems, depending on the ingredients and care used in proportioning and placing it.

The two essential requirements of quality concrete are strength and durability. A proper balance between these two characteristics is necessary in order to get a good, strong foundation. In order to achieve this balance, four steps must be properly completed:

  1. Selection of materials
  2. Proportioning of materials
  3. Placing and finishing of concrete
  4. Curing of concrete

Selection of Materials

The materials used in making concrete are water, aggregates (sand and gravel), portland cement, and admixtures.

There are several types of portland cement available for different types of jobs. However, we are mainly concerned with the normal Type I portland cement, as it is the one most commonly used on construction of foundation and floors.

Together with the water, aggregate and cement, additional elements are sometimes required in the concrete to help make it react differently. These elements are called admixtures. One such admixture is used to accelerate the rate of early strength gain so that forms can be removed earlier. This reduces the time it usually takes before concrete can be finished, also known as the appropriate curing time.

In addition, there are other ingredients, which can be added, such as air infiltrating agents used for roadwork, where the concrete must be resistant to salts and freezing. Retarders are sometimes used during hot weather so that concrete may be moved from the mixer to its final position before the initial set takes place.

Proportioning of Materials

Quality concrete inherently possesses high compressive strength. If a tensile strength is desired, steel reinforcing bars must be embedded in the concrete to resist this tension. Tensile strength is the resistance to stretching or drawing out of the concrete. The most important, single consideration in obtaining the desired strength of concrete lies in the proper proportioning of the materials.

The compressive strength is usually defined in terms of so many pounds per square inch in 28 days, which is the norm for concrete to reach its designed strength. A typical batch of concrete with a specified strength of 3,000 psi at 28 days would have approximately these proportions:

  • Cement 94 pounds
  • Sand 185 pounds
  • Coarse Aggregate 360 pounds
  • Water 5 1/2 gallons

Practically all concrete is machine mixed in a rotating drum cylinder, either in a "Ready-Mix" truck, or a similar mixer on the job site.

Placing and Finishing of Concrete

Concrete Pouring Photo

No element in the entire cycle of quality concrete production requires more careful consideration than the final operation of placing and finishing. Placing and finishing are both dependent on workmanship, so here, care and skill are especially important.

Forms hold the concrete in place until it has hardened. They are usually constructed of wood or metal, and must be rigid enough to support the weight of the concrete without deformation or appreciable deflection, and should be tight enough to prevent the seepage of water. The concrete is deposited uniformly in order to prevent segregation of the aggregates and to make certain the reinforcing steel is completely covered without voids. Concrete is conveyed from the mixer to the forms by means of barrows, by inclined chutes, or is pumped. Normally, the concrete is vibrated by an electric or pneumatic vibrator or spaced to assure well, uniform coverage, and to prevent honeycombing from occurring. In placing concrete in deep layers, a gradual increase in water content in the top layers usually results from the increased pressure on the lower portion. This excess water is called Latinate, and should be removed before further finishing, because it produces lower strength concrete in the upper levels if permitted to remain.

When pouring concrete floor slabs, the surface is screeded prior to finishing. Screeding is the process of striking off the excess concrete to bring the top surface to proper contour and elevation. A template is moved back and forth on the forms, with a sawing motion, to force concrete into the low areas.

After the foundation or floor is roughly leveled, the surface is ready to be finished. Wood or metal floats are used initially to compact the concrete, forcing the larger aggregates below the surface. Steel trowels are then used to obtain a smooth surface and to compact it for a hard finish. If there are areas exposed to outdoor usage, such as walks or driveways, a broom finish is recommended. The broom finish is simply taking a broom and wiping it across the concrete. This roughens the surface for a friction grip, so that the concrete is not slippery when wet.

Curing of Concrete

Concrete hardens because of the chemical reaction between portland cement and water. This process continues as long as temperatures are favorable and moisture is present.

The quality of concrete, or the strength of the concrete, is dependent on the temperature and moisture conditions in which it cures. In addition, its resistance to abrasive action is also increased by these same elements in curing.

While it is important that the amount of water used in mixing be controlled so that the consistency is as nearly normal as practical. It is just as important that concrete is not allowed to dry out too soon or it will reach strength less than 50% of its potential.

Temperature has a considerable effect on the rate of hardening. In the past, you could not pour concrete during the winter season because the water in the mixture would freeze and prevent the proper setting. But now, construction operations may continue throughout the year. The most favorable conditions are between 50 and 90 degrees Fahrenheit. However, good curing temperatures may range below 50 F and even below 32 F, if the concrete is properly protected from cold air during the first 72 hours after being placed.

With suitable precautions, concrete can be placed during cold weather and have the same qualities as concrete cured during the summer months.

Foundations

Concrete Foundation Photo

The actual construction of a building must obviously begin with the laying of the foundation, a necessary base for any structure. Because all ground, regardless of the bearing value of the soil, has a tendency to move, the building must be built on a good, strong foundation that is designed for the anticipated loads.

The old saying, "a building is only as strong as its foundation" is still just as true today as it was years ago when someone coined that phrase. While materials and methods are much improved, faulty foundations remain a paramount source of trouble for some building construction. Leaky basements, cracking walls, and settling floors are typical trouble spots. And once they exist, they can present some of the most difficult problems to solve.

Foundations are actually broken down into two classifications:

  1. Walls
  2. Footings

A foundation wall means any wall with a major portion located below the grade level. The wall serves as a base support for other walls and columns. A footing is a structural unit used to distribute building loads to the bearing materials.

Foundations used for rigid frame buildings are considerably different from those normally required for conventional structures with load-bearing walls. The choice of foundation is determined in part by the basic loads, which need to be resisted.

Foundations for metal buildings are usually not subject to extremely heavy vertical loads; however; they are required to withstand horizontal loads of considerable magnitude. Horizontal loads tend to push out the foundation, and if not adequately provided for, they could cause failure not only of the foundation, but also of the main structural framing members. These loads are resisted by two methods:

  1. Use of steel tie-bars. The reinforcing bars are connected to anchor bolts, providing a continuous tie between the column bases.

    A spread tie, or hairpin, which transfers the load from the column anchor bolts to the welded wire fabric (used in floor slab) is used where the horizontal loads are not large. Basically, it utilizes the same design principle as the tie-bars.

  2. Increasing size of footing. Increasing the size of the footing helps counteract the force exerted by horizontal loads, thus preventing the movement of the foundation. This method is usually the most expensive.

The type of foundation depends upon the geographical location of the building, topography of land, frame loads imposed on foundation, local building code restrictions and architectural considerations. Generally, there are three types of foundations used with our building systems:

  1. Floating Slabs. Floating slabs consist of a concrete slab, monolithically poured with a continuous grade beam. The grade beam is either spread directly under the column or reinforced along the bottom to carry the vertical column loads.

  2. Pier, Footing, and Grade Beam consist of a square or rectangular footing and a grade beam wall. A drilled pier may be utilized in lieu of the square or rectangular footing. Piers and footings carry most of the vertical loads.

Floors

A floating slab, or slab on grade, is the general type of floor system often used with metal buildings. It is either poured monolithically with the foundation wall, or poured after the foundation wall is in place. In both cases, the concrete slab encases steel serving as reinforcement. This steel reinforcing reduces the cracking of the floor and helps control expansion and contraction.

Where there are additional concentrated-load requirements standard reinforcing bars are often necessary.

Many floor slabs are constructed with a vapor barrier to prevent passage of moisture from the soil through the concrete. The most common barrier used is a polyethylene sheet material. This is placed on top of a gravel or sand base, with the concrete being poured directly over the material.

The type of floor system required and the thickness of floor depend on what loads are anticipated. The average of these floor loads is uniformly distributed. Any concentrated load, such as machinery or storage racks, and any moving load, such as forklift trucks, must be considered in order to establish the floor design.

Many local building codes establish minimum floor-design loads for various end uses.

Another consideration in the floor design is the type of joints used. A construction joint is simply a joint required where construction begins and ends, from one day's pour to the next.

An expansion or control joint is used where the floor slab abuts a wall or where a steel column or pier passes through the floor. It is used to control the contraction that will occur, by merely forcing the crack to occur at a predetermined point. Actually, an expansion joint in a concrete foundation might better be classified as a contraction joint because during the curing process, the concrete shrinks in volume approximately the same amount that would normally result from a 100 degree drop in temperature.

If the finished concrete floor is to be sealed, hardened, or waterproofed. Chemicals or additives are often applied during the final finishing or soon after curing to achieve the results desired.

Pre-Assembly

In the pre-assembly phase, there are several things that are necessary to consider: access to the site, assuring sufficient workspace requirements at the site, availability of required utilities, a comprehensive safety awareness program, and a familiarity with the erection drawings.

The vehicle transporting your building parts must gain access to the building site from the adjacent highway or road. Such access should be studied and prepared in advance of arrival. All obstructions, overhead and otherwise, must be removed and the access route graveled or planked if the soil will not sustain the heavy wheel loads.

Inspect to insure that there is enough room to physically perform the tasks required to erect the building. Application of sheeting and trim can be expensive when there is not sufficient working space because of the proximity of adjacent buildings or other obstructions.

The availability of any required utilities should also be considered in advance. Take careful note of any overhead electric lines or other utilities to avoid hazards and damage (notify your utility company when necessary).

Develop a comprehensive safety awareness program in advance to familiarize the work force with the unique conditions of the site, and the building materials, along with the appropriate "Safe Work" practices that will be utilized.

Finally, before assembly of the building can commence, you and your crew must familiarize yourselves with the erection drawings furnished with every building.

Each plan is specially prepared for each individual building and should be strictly adhered to.

Assembly of the Building

The next stage in the construction process of a building is the assembly of the structural and covering systems. We will merely discuss the general steps in this process. One of the best ways to become familiar with this phase is to visit an actual construction job within your local area.

Unloading and Layout of Material

Pre-planning of the unloading operations is an important part of the assembly procedure. This involves careful, safe and orderly storage of all materials. Detailed planning is required at the job site where storage space is restricted. Here, a planned separation of materials in the order of assembly process is necessary to minimize the costly double handling of materials. While set procedures are not possible in all cases, special attention should be given to the following items:

  1. Location of carrier vehicle during unloading. Unload material near their usage points to minimize lifting, travel, and rehandling during building assembly.

  2. Prepare necessary ramp for truck. The edges of the concrete slab should be protected to minimize the danger of chipping or cracking from truck traffic if the materials are to be laid out on the slab. One important safety consideration is the fact that materials stored on the slab may subject the workers to possible injury from falling objects.

  3. Schedule lifting equipment. The manufacturer neither supplies lifting equipment nor labor to unload the truck. The type and size of lifting equipment is determined by the size of the building and the site conditions. The weight and size of the largest piece of structural steel is to be lifted as high as it has to be lifted and the distance of the lift from the position of the crane all impact the selection of the crane or other lifting equipment. Length of boom, capacity and maneuverability of lifting equipment will determine its location for both unloading and assembly.

    Use the same lifting equipment to unload and erect structural parts of the building if possible. Combining the unloading process with the building erection usually minimizes lifting equipment costs. As soon as the truck is unloaded, the lifting equipment should start erecting the columns and raising the assembled rafters into position.

  4. CONSIDERATION OF OVERHEAD ELECTRIC WIRES. OVERHEAD POWER LINES ARE A CONTINUING SOURCE OF DANGER. EXTREME CARE MUST BE USED IN LOCATING AND USING LIFTING EQUIPMENT TO AVOID CONTACT WITH POWER LINES.

  5. Schedule crew. Depending on the crew size, valuable time can generally be gained if the supervisor plans and watches ahead instead of getting tied up with a particular unloading chore.

  6. Check Shipment. When shipments are received in the field, two inspections are necessary:

    1. When items, boxes, crates, bundles or other large components are received and unloaded for the carrier, they should be checked off from the packing list. If during the inspection, damages, or shortages of items are found a report should be filed with the carrier immediately at the site. When damages are evident from the exterior of containers, they should be opened and inspected thoroughly at the time of receiving shipments.

    2. When bundles, crates, cartons, boxes, etc. are opened following delivery, another check must be performed to determine the quantity received and their condition. If during this inspection damages or shortages of items are found upon opening the crates or cartons, a written claim should be filed no later than fourteen days after delivery. If a shortage is discovered within a container, then a written notice should be mailed or faxed to SBS. Unless these two important inspections are made and any reports or claims are filed immediately, settlements become very difficult and usually all parties suffer the loss.

Location of Building Parts

Columns and rafters are usually unloaded near their respective installed positions on wood blocking on the slab in position for easy assembly.

Endwalls are usually laid out at each end of slab with the columns near respective anchor bolts.

Hardware packages should be located centrally, usually along one sidewall near the center of the building. This will minimize walking distances to other parts of the slab area.

Purlins and girts, depending on the number of bundles, are usually stored near the sidewalls clear of the other packages or parts.

Sheet packages are usually located along one or both sidewalls off the ground and sloping to one end to encourage drainage in case of rain.

Accessories are usually unloaded on a corner of the slab or off the slab near one end of the building to keep them as much out of the way as possible from the active area during steel erection. All materials should be protected from the elements and walking on materials should be avoided at all times.

Storing Materials

Structural Framing Members

A great amount of time and trouble can be saved if the building parts are unloaded at the building site according to a prearranged staging plan. Proper location and handling of components will eliminate unnecessary handling.

Blocking under the columns and rafters protect the splice plates and the slab from damage during the unloading process. It also facilitates the placing of slings or cables around the members for later lifting and allows members to be bolted together into subassemblies while on the ground.

If water is allowed to remain for extended periods in bundles of primed parts such as girts, purlins, etc., the pigment will fade and the paint will gradually soften reducing its bond to the steel. Therefore, upon receipt of a job, all bundles of primed parts should be stored at an angle to allow any trapped water to drain away and permit air circulation for drying. Puddles of water should not be allowed to collect and remain on columns or rafters for the same reason.

Wall and Roof Panels

The Manufacturer's wall and roof panels including color coated GalvalumeĀ® and galvanized, provide excellent service under widely varied conditions. All unloading and erection personnel should fully understand that these panels are quality merchandise, which merits cautious care in handling and storing.

Under no circumstances should panels be handled roughly. Packages of sheets should be lifted off the truck with extreme care taken to insure that no damage occurs to ends of the sheets or to side ribs. Please note the designated "pick points" to prevent crimping damage during lifting of bundles. The packages should be stored off the ground sufficiently high to allow air circulation underneath the packages. One end of the package should always be elevated to encourage drainage in case of rain.

All stacked metal panels are subject, to some degree, to localized discoloration or stain when water is trapped between their closely nested surfaces. The Manufacturer exercises extreme caution during fabricating and shipping operations to insure that all panel stock is kept dry. However, due to climatic conditions, water formed by condensation of humid air can become trapped between stacked sheets. Water can also be trapped between the stacked sheets when exposed to rain. This discoloration caused by trapped moisture is often called wet storage stain.

Use wood blocking to elevate and slope the panels in a manner that will allow moisture to drain. Wood blocking placed between bundles will provide additional air circulation. Cover the stacked bundles with a tarp or plastic cover leaving enough opening at the bottom for air to circulate.

Metal Building Assembly

Responsible personnel, experienced in rigging and handling light steel members in a safe manner should complete the layout, subassembly, and assembly of the metal building. Improper handling can easily result in injury, delays and unexpected added costs. This is particularly true when raising assembled rafters for wide buildings.

The assembly crews should always use proven and safe erection methods. Knowledge of and adherence to OSHA and other local codes or laws governing jobsite safety is critical, and is the responsibility of the erector.

Tips to Keep Assembly Costs Down

Minimum costs should be obtained when the following conditions are met during the assembly of a building:

  1. When safety practices are discussed and initiated in advance of any work procedure.

  2. When the overall work of assembling the building is divided into individual jobs, and when each job is assigned to teams of workers consisting of two to seven workers each, with three to five worker teams preferred.

  3. When individual workers are properly trained and instructed in advance as to what they are to do and the safe way to do it. This eliminates time wasted while waiting to be told what to do next.

  4. When building parts are properly laid out according to advanced planning so as to avoid lost time in repetitive handling or in searching for specific items.

  5. When as many parts as can be safely raised in a single lift are bolted together in subassemblies on the ground where assembly work is faster and safer, thereby, requiring fewer lifts and fewer connections to be made in the air.

  6. When assembly of the steel framework starts at one end and continues bay by bay to the other end of the building.

  7. When the first bay is completed, the individual frames are erected and tied together by skeleton or lead purlins and the fill-in purlins are installed after the costly lifting equipment has been released.

  8. When the proper tools and equipment are available in sufficient quantity and in good/safe working condition.