Erection Bracing of Low-Rise Structured Steel Buildings

In high-rise construction and bridge construction the need for predetermined erection procedures and temporary support systems has long been established in the industry. Low-rise construction does not command a comparable respect or attention because of the low heights and relatively simple framing involved. Also the structures are relatively lightly loaded and the framing members are relatively light. This has lead to a number of common fallacies which are supported by anecdotal evidence. This article will guide you how to carry out the erection of steel structures for low-rise buildings step by step.
Three of the most important things that are to be noted before starting the job is as follows
(a)    After receiving the building package and before storing, all the items are required to be checked for any defects and quantities as per the list, if a single part is missing, the entire work will suffer. Hence the owner should make a check list of all the items and verify it while receiving.
(b)    Materials needs to be properly stored and handled at site during construction to avoid any undue damage.

(c)    The owner should ask the contractor an erection plan as well as safety action plan for executing the job.
Following are the broad steps for erection of bracing and other parts of low-rise structured steel buildings
A.     Site and Foundation Preparation
B.     Building Delivery and Storage
C.     Erection of Primary, Secondary Structural and Doors and Windows
D.     Sheeting (Wall and Roof)
A. Site and Foundation Preparation
Before doing the concrete foundation it is extremely important that foundation should be properly checked for its width and length and most importantly for equality of both the diagonals. After this all the column locations to be marked on the foundations very accurately and anchor bolts to be fixed then. This is a very important step, as any mistake in this step will effect the entire erection programme, since all the structures are fabricated for predetermined sizes and mistake in any span would give birth to complexity in the erection process. Hence great care to be taken while carrying out the anchor bolt setting plan. All anchor bolts should be held in place with a template or similar means, so they will remain plumb and in the correct location during placing of the concrete. Check the concrete forms and anchor bolt locations prior to the pouring of the concrete. A final check should be made after the completion of the concrete work and prior to the steel erection. This will allow any necessary corrections to be made before the costly erection labor and equipment arrives.
 
B. Building Delivery and Storage
While receiving the materials at site, place the parts around the foundation so they will be in the most convenient locations for installation. For example: place the end columns and rafters at the ends of the building and the mainframe columns and rafters at the sides. Place the bolts and nuts in a place where they will be accessible to the parts. You may want to screw the bolts and nuts together and place them with the corresponding parts. This will save time as you begin assembling the parts and also will reduce your time and cost for re shifting the materials again to the location of erection. Purlins and girts, depending on the number of bundles, are usually stored near the sidewalls clear of 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. For storage of sheets it is recommended to be stored under roof if at all possible. If sheets are to be stored outside, the following precautions should be observed:
1.     The storage area should be reasonably level, and located so as to minimize handling.
2.     When stored on bare ground, place a plastic ground cover under the bundles to minimize condensation on the sheets from ground moisture.
3.     Store bundles at least 12 inches above ground level to allow air circulation beneath the bundle, and to prevent damage from rising water.
4.     Elevate one end of each bundle slightly to permit runoff of moisture from the top of the bundle or from between sheets. A waterproof cover should be placed over the bundles to allow for air circulation under the cover.
5.     Inspect stored bundles daily and repair any tears or punctures in the waterproof cover.
6.     Re-cover opened bundles at the end of each workday to prevent subsequent moisture damage.
C. Erection of Primary, Secondary Structural and Doors and Windows
 
General
Many methods and procedures are in use for erecting the structural portion of metal buildings. The techniques of raising frames vary from erecting small clear spans and endwall frames in units to erecting the larger clear spans and modular frames in sections. The erection methods used depend strictly on the type of building, the available equipment, the experience level of the crews, and the individual job conditions. The variations in these factors preclude the establishment of a firm or specific set of erection rules and procedures. Consequently, the erection operation must be tailored by the erector to fit individual conditions and requirements. However, there are certain erection practices, pertaining to structural members, which are in general use and have
proven sound over the years and which can be followed for erection in all the places. In every condition Erectors are cautioned not to cut primary members (rigid frame columns, rafters, end bearing frame rafters, interior columns). These are the primary support members for the frame and are designed as such. Any cutting of these members may affect the structural stability.
The intermediate or interior frames nearest the bearing endwall are usually erected first. This bay usually contains the diagonal bracing. The proper completion and plumbing of this first bay is extremely important to the successful completion of the building.
Although several methods are used to erect rigid frames, it has been found
most satisfactory to erect the columns first, tie them together with the girts and tighten the anchor bolts. On small spans and short eave heights, columns can often be set in place by hand without the use of hoisting equipment. Temporary bracing should always be installed as soon as sections are lifted in place (See Figure 1). Once this is over the structure is ready for girt erection. At first it is needed to put one screw in the end of each girt.
At the corners put 2 screws in the end of the girts. The girt erection is shown in Figure 2a and 2b.
Once the sidewalls have been stood and all girts are on them, wind rod braces needs to be installed (See Figure 3a and 3b). These go in the same bay on both sides, preferably near the center of the length of the building. Care should be taken that these are not installed where there is a door or window opening. Once installed, these can be used to adjust the columns to be plumb. Once the columns are plumb make sure everything is snug.
    
After this attach the girts to the clips on the column and end wall legs using a single tek screw in each end. After ensuring that columns are straight then only attach the knee braces to the girts. The knee braces will bolt to the column or truss and attach to the girt with a tek screw. If columns are twisted it is needed to straighten them before attaching the knee brace (See Figure 4).
After erection of columns and installation of girts on the sidewalls the structure is ready for the roof trusses erection (See Figure 5,6). Roof trusses should be bolted together on the ground and lifted into place. Two important point to be noted before truss erection is as below
    
(a)    Knee brace angles should be installed on the truss before lifting into place.
(b)    If building is wider than forty feet it is recommended that a spreader bar should be used to pick up the trusses. If it is not used, the truss may fold in the middle and cause damage.
Knee brace fixing to the roof truss and attaching roof truss to the legs is shown in Figure 7 and 8 below.
    
     
Attaching purlins to the truss top with joint details is shown in Figure 9 and 10
Installation of wind braces in the roof truss in the same panel where it is attached in the wall is shown in Figure 11. Figure 12a and 12b shows installation of eave clip to the end of pulin.
How to Make a Framed Opening (See Figure 13a and 13b)
1.     Measure the size of the door or window to determine the size opening required.
2.     Mark the girts where you want to position the opening.
3.     Cut the girts with your abrasive saw.
4.     Slide the track over the end of the cut girts to form the opening.
5.     Insert the door or window into the opening and square it so that it functions properly.
6.     Fasten the track to the girts with tek screws and fasten the door or window to framed opening.
7.     Attach J trim with colored screws if it isn’t part of the door or window frame.
Once this step is complete the sheeting job can be started. However before proceeding for sheeting job, it is necessary to recheck and make sure everything is properly installed at this point. If anything is missing it is the time to go back and fix it before sheeting job is started.
    
Checklist for the erection job (To be carried out prior to start if sheeting job)
1. Columns and Endwallcolumns
-    All columns are properly located
-    All columns are plumb
-    All bolts are in place and tightened
    
2. Roof Trusses
-    All roof trusses are properly in place
-    All bolts are in place and tightened
-    Building is plumb
3. Purlins and Girts
-    All purlins and girts are in place and well attached
-    Fascia purlins are installed
-    6” gable track is installed
4. Bracing
-    All knee braces are bolted and tightened on columns and roof trusses
-    All knee braces are screwed to girts and purlins
-    All wind brace rods are in place
-    All wind brace rod nuts should be snugged down against the clip after building is plumb
D. Sheeting (Wall and Roof)
After completing the check the structure is ready for sheeting erection. Gang drill is recommended for drilling the sheets. The process is shown in Figures 14, 15 and 16. Not more than 20 sheet panels to be stacked together.
Wall panels are installed before roof. Base trim must be attached first with 4 screws per piece. At every location the verticality of the wall panel is to be checked.
Once the wall panel is installed, next step is installation of roofing sheets (See Figure 18). After the roofing installation it is required to check whether all the bolts caps and washers are in place or not otherwise there is possibility of leakage during rains.
Final step is to put the corner corner trim and gable trim (See Figure 19a) and end cap ( See Figure 19b).
Conclusion
It is recommended to go through across the building after completion of the work to ensure that there are no missing screws or loose parts. Everything should be checked twice to make sure it is tight and secure. During the entire construction period the owner should look after the safety aspect of the work very carefully viz. personal protective equipment’s are allotted to every worker or not, safety nets are there or not, lifting capacity of the crane/chain pulley etc. It is also recommended to make a proper work schedule day wise before starting the work in along with the contractor which will help the owner to keep a track on the erection process and avoid getting undue delay in the work.