Secondary Structural Framing

Purlins, girts and eave struts are secondary structural members used to support the wall and roof panels. Purlins are used on the roof; girts are used on the walls and eave struts are used at the intersection of the sidewall and the roof.

Secondary members have two other functions: they act as struts that help in resisting part of the longitudinal loads that are applied on the building such as wind and earthquake loads, and they provide lateral bracing to the compression flanges of the main frame members thereby increasing frame Capacity. Purlins are bolted to the top flanges of rafters and to each other at purlin laps by means of machine bolts conforming to ASTM A307 M Type A.

Roof and wall panels are laid perpendicular to the roof purlins and wall girts, respectively, and fastened to them by means of self-drilling fasteners. For Clear Span (CS) and Multi-Span (MS) buildings the sidewall girts are by-pass connected (by framed) to the outer flanges of the exterior columns and are lapped at each interior rigid frame column.

For Space Saver (SV) and Lean-To (LT) buildings, the sidewall girts are flush connected (flush framed) so that the outer flange of the girt is in the same plane as the outer flange of the exterior columns.

Endwall girts of all standard buildings are flush connected so that the outer flanges of the girts are in the same plane as the outer flanges of the endwall posts.

Basic Structural Systems The strength of the pre-engineered building system lies in its ability to incorporate a large number of structural subsystems that use standard components and standard design approaches to satisfy a wide range of custom requirements. The structural subsystems that form a basic Zamil Steel pre-engineered building consist of:  • Bracing Systems • Secondary Members • Post & Beam Endwalls Structural subsystems use the same three basic product categories; built-up “I” sections, cold formed “Z” sections and cold-formed profiled sheeting panels, to produce economical solutions to functional & aesthetic requirements. This chapter also displays the standard details adopted by Zamil Steel for these subsystems. These details were developed as a result of the extensive experience gained by Zamil Steel during the past 20 years and have proven, time after time, to result in safe and economical solutions using components that are easy to engineer, easy to fabricate and easy to erect. Zamil Steel’s extensive engineering resources and capabilities enable us to adopt any proposed detail to meet a customer’s unique requirements. We recommend that you read the following Zamil Steel publications in conjunction with this chapter: • Standard Product Specifications • Panel Chart (colors & profiles) At Zamil Steel we make it a point to continuously review and enhance the details shown in this chapter. Our purpose is to develop details that are more economical, more fabrication friendly and more erection friendly. We strongly embrace the partnering concept of doing business and we acknowledge that

most improvements are the result of feedback from concerned well-meaning customers. Thus, we sincerely solicit your views and suggestions to improve our product and welcome any improvements you may suggest.

Bracing 
Lateral stability along the width of a pre-engineered steel building, is provided by designing the frames to resist the imposed lateral loads. Bracing systems are furnished along the length of the buildings to provide longitudinal stability due to the weakness of the building structure in that direction. The main purpose of a bracing system is the transmission of lateral forces due to wind, cranes, earthquakes, etc. from their point of application on the structure to the column bases and eventually into the foundations. Zamil Steel standard bracing systems are Diagonal X-Bracing, Portal Bracing and Minor Axis Bending.

Diagonal X-Bracing
This is the standard bracing system commonly used in the roof and sidewalls of pre-engineered steel buildings. Members used for the diagonals are galvanized cable strands (Zamil Steel’s standard), solid smooth rods, flat bars or angles.

 Portal Bracing
This form of bracing is usually provided between exterior columns at the exterior sidewalls, or between interior columns in very wide Multi-Span and Multi-Gable buildings, in bays where diagonal X-bracing is not permitted due to a desire to have clear non-obstructed deep space through these bays. Portal frames are made from built-up columns and rafters. Portal frame columns are commonly stitch bolted to the web of the Rigid Frame columns as an alternative to anchoring the portal frame columns to the foundation substructure.

Minor Axis Bending
In this method the Rigid Frame columns are analyzed as fixed at the base, in the minor axis direction, so as to resist the lateral forces applied along the length of the building. This system is recommended only in buildings with narrow widths, low eave heights and containing a large number of bays. The lateral force along the eave of the building is divided by the total number of mainframe columns, resulting in a force per column that is small enough to be resisted by the sectional properties of the column along its weak axis. Minor axis bending becomes uneconomical and unsuitable for buildings with large widths, high eave heights, and a small number of bays. Minor axis bending is most common in shade structures (mostly car parking structures) which require walls to be fully open for access. These structures are usually long, have low eave heights and consist of a large number of bays.

Endwalls  The Endwall Frame of a pre-engineered building may be designed as a main Rigid Frame (R.F.) i.e., similar to an interior frame, or as a Post-and- Beam (P&B) frame. Post-and-Beam Endwall   The Post-and-Beam endwall system of framing consists of columns (posts), with pinned ends, supporting endwall rafters. Girts are flush-framed between posts to provide lateral stability and a neat appearance. Post-and-Beam endwalls are assumed to be laterally stiff due to the flush-framed girts and the diaphragm effect of the wall sheeting. The diaphragm action is proven to be sufficient enough to resist the transverse wind force acting on the small tributary area of the sidewall. Where a blockwall is required in place of the wall sheeting, angle clips are provided at certain locations along the posts to tie them to the blockwall in order to ensure the frame’s stability. Endwall posts are designed to carry both vertical loads and horizontal wind loads.   Rigid Frame Endwall  A Rigid Frame endwall is typically used when a building is designed for a future  expansion along the length of the building, when a crane system (runway beam) extends to the end of the building or when large unobstructed openings are required in the endwall. This type of frame is usually designed to withstand a full bay load and is normally identical to an interior main rigid frame. When a main rigid frame is used, a distance of 385 mm is maintained between the centerline of the main frame column and the outside flange of endwall posts (i.e. the endwall steel line). This is to provide sufficient lap for purlins and girts in case of a future expansion. Endwall posts provided in this type of framing system are designed to carry horizontal wind forces only. Standard endwall post spacing is 6 m, but this may be changed to accommodate special needs such as very wide doors.

A J ack beam is a horizontal structural member. It normally spans between two alternate frames in order to support the roof rafter of the intermediate frame at a column location when that column has to be removed to provide clear space at the finished floor level. Within exterior walls, jack beams are required when a bay longer than 10 m is desired along the length of a building. This is sometimes necessary when a long bay is specified due to frequent movement of large equipment or trailers that load and unload materials inside a factory or a warehouse. The use of jack beams allows bay lengths of up to 20 m. In the interior, jack beams are encountered at the top of interior columns of Multi-Span buildings when one or more of the interior columns must to be removed to provide clear space at the finished floor level. Zamil Steel jack beams can be straight or tapered built-up sections and are designed to support vertical and horizontal loads when used in exterior sidewall applications, and vertical loads only when used in interior Multi-Span applications.

Expansion Joints Materials expand when heated and contract when cooled. The amount of expansion or contraction depends on the type of the material and its molecular structure. The coefficient of linear thermal expansion is a measure of the incremental increase in the length of a member per unit length resulting from a single unit increase (°C or °F) in temperature. When a member is restrained from free movement during expansion or contraction, stresses develop in the member. These thermally induced stresses may be compressive or tensile depending on whether the restrained member is undergoing expansion or contraction. If these additional stresses are not considered in the design of that member, failure may occur. Thus, expansion joints are provided at certain intervals along a member to absorb accumulated incremental movements resulting from temperature changes during the life of the structure.   In steel construction proven guidelines exist for calculating the required distance between expansion joints and for determining the type of fastener slots that must be provided to insure that the structure can expand and contract freely.    A safe but very expensive practice for releasing Longitudinal thermal stress requires the provision of double rigid frames at expansion joint locations. We believe that this is unnecessary unless there is a requirement for a firewall at the longitudinal expansion joint location. Zamil Steel’s standard practice for releasing excessive Longitudinal thermal stresses is to use only one rigid frame at the location where an expansion joint is required and to provide slotted purlin holes at the location of the expansion joint that can absorb thermal movements at that point.

Block Wall

As a normal practice the walls of a Zamil Steel building are sheeted with pre-painted Zincalume panels available in a range of standard colors. Pre painted panels are economical, attractive and easy to install. However, in some applications, clients find it necessary to specify a partial height or full height masonry wall or blockwall. The most common reasons for choosing a blockwall are when:

• Storage inside the building might be placed against the exterior walls of the building.
• Stored material, if in contact with wall panels, might initiate or encourage steel corrosion.
• Heavy forklift activity outside the building may accidentally dent the metal walls.
• There is a desire to buy locally made accessories (personnel doors, louvers, windows, etc.) that are designed primarily for blockwalls.
• A blockwall is needed for architectural reasons. 

Although the provision for a blockwall or a masonry wall is an option, Zamil Steel has developed many standard details for buildings with masonry walls or a combination of masonry and sheeted walls.

When an endwall is open (unsheeted) for blockwall, up to a certain elevation, Zamil Steel requires that the endwall posts be tied to the blockwall at standard girt locations, or at a maximum spacing of 2 meters, along the full height of the blockwall, in order to maintain adequate bracing of the endwall posts.

When this situation occurs in sidewalls, Zamil Steel’s practice is to design the columns for a freestanding condition (unbraced) up to the full height of the blockwall.

Foam closures, trims and flashing are provided at the transition between the wall sheeting and the masonry wall in order to provide a watertight joint and a neat finished appearance.

When considering the partial removal of the metal wall sheeting, it is important to know the standard location of wall girts so that an economically sound decision can be made. The location of the first wall girt is at 2.25 meters above the finished floor level and this is the most economical height for blockwalls in a standard Zamil Steel pre-engineered building.

Pre Cast Panels  

Precast concrete panels are one of the numerous types of wall systems that can be easily integrated and are very frequently used with pre-engineered steel buildings. Zamil Steel does not supply precast panels, however, many standard details for precast concrete walls or a combination of precast concrete walls and sheeted walls have been developed. Even though precast concrete panels are more expensive than cast in-situ concrete and concrete block, they offer several advantages: Precast panels can be sized, shaped and textured to suit the architectural requirements of the buildings. Installation of the precast panels is faster and easier. Precast panels are prepared in controlled environments versus cast in-situ concrete that requires extensive on site supervision and inspection. Lengthy casting and curing times on-site are not required since, precast panels are produced off-site. Precast panels are self-supported on the ground. Horizontal structural members are supplied by Zamil Steel on the wall to provide lateral stability. Zamil Steel also supplies special brackets to support precast panel fascias.   In order to accommodate the precast wall system in the design and detailing of the pre-engineered steel building, clear sketches should be submitted to Zamil Steel, at the quotation stage. The sketches should clearly illustrate the exact dimensions of the precast panels and the details of the fixing points.   It is also important to provide Zamil Steel with the name of precast concrete supplier and his project manager in-charge, in order to obtain other details related to their precast system such as loading conditions, fixing system, etc.   For further information consult any Zamil Steel representative.

Exterior Roof and Wall Panel Details

Exterior single skin panels are used on the roofs and walls of structures to provide a protective outer shell. Zamil Steel offers three different profile options for single skin roof and wall panels. They are: Profile “B”, Profile “R” and Profile “A”. The choice of the profile is primarily dependent on aesthetic preference, economy and the level of expertise of the erection crew.   Since all these panels use the same raw material coil width, a panel with more ribs or deeper ribs will generally have a narrower width (coverage area), a higher load capacity and a higher price.   The standard Zamil Steel roof and wall panel profiles have been selected on the basis of optimizing value without sacrificing function. Optional panels are also available and are viable in some applications and situations.

Liner panels are used to conceal the roof purlins, wall girts and fiberglass insulation on the inside of roofs and walls of pre-engineered buildings where a neat and smooth finished appearance is desired. The standard Zamil Steel liner is a Profile “R” panel, which is the most economical and most popular panel especially for use in factories, warehouses, aircraft hangars, and general industrial buildings. Optional liners include Zamil Steel’s Profile “B”, Profile “A”, Profile “D” and Profile “E” panels which are available upon request.