What is the difference between a purlin and a girder

I think. I have always thought of them as one and the same myself. Definition of GIRDER : a horizontal main structural member as in a building or bridge that supports vertical loads and that consists of a single piece or of more than one piece bound together Definition of BEAM : a long piece of heavy often squared timber suitable for use in construction.

Joined Oct 25, Messages 11, Location So. Girders are collector beams. Girders support beams. Sometimes "Girders and beams" are mislabled as purlins. Rio Silver Member. Joined Mar 31, Messages From the Dictionary of Architecture and Construction : Girder- A large or principal beam of steel, reinforced concrete, or timber; used to support concentrated loads at isolated points along its length.

Rio said:. Click to expand Beam support a distributed load where girders can support point loads and distributed loads. Arrows are conveniently stamped on both the purlins and girts and point to the larger leg or flange for easier installation. Another structural member of your building similar to girts and purlins are eave struts. Eave refers to the line along the sidewall formed by the intersection of the planes of the roof and the wall.

Already a Member? Join your peers on the Internet's largest technical engineering professional community. It's easy to join and it's free. Register now while it's still free! Already a member? Close this window and log in. Join Us Close. Are you an Engineering professional? Join Eng-Tips Forums! Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top.

Purlins are 2 by 4 feet and are installed much like metal roofing. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. Purlin laps must be bolted in the top web hole and the lower flange holes at both ends of the lap as shown below. Bolting only in the web of lapped purlins does not provide full structural continuity and excessive loads could be placed on to roofing screws that penetrate both purlins within a lapped region.

If the lower web hole in a lap is used for attaching fly bracing ensure that an additional bolt is used. Design Station Bridging can be installed either up or down the roof slope but cannot be mixed within a bridging run.

Girt bridging must not exceed its compressive capacity. Where more than one row is to be installed always complete the bridging for each girt before commencing on the next i. The welding or hot cutting of purlins, girts or bridging is not recommended. The heat produced in welding will affect the material properties of the high yield strength cold-formed steel used in purlins. In many instances considerable stress concentrations are likely to arise, even with good quality welding.

In addition, welding will locally remove the protective coating, leading to a potential reduction in durability. Roof Purlins must be kept dry during storage as water present between close stacked sections will cause premature corrosion. If they become wet, they should be separated and stacked openly to allow for ventilation to dry the surface.

The installation of Purlins can be hazardous and will require an adequate safety plan be in place prior to handling or installing of these products. All rigging, scaffolding and safety equipment must comply with the relevant codes, Australian standards and statutory requirements.

It is recommended that good trade practice be followed such as that outlined in Australian Standards AS Guidelines for the erection of building steelwork and HB39 Installation code for metal roof and wall cladding. Normally, purlins are not designed to be walked on unless fully covered by correctly installed roofing materials or the correct grade of safety mesh. The manufacturing or delivery process may result in oil or grease adhering to these purlins which could increase the potential hazard.

Handling of this product must be carried out using a correctly supervised crane or appropriate lifting device. Safety harnesses must always be used during installation of purlins when working off the ground, and under no circumstances must any body weight be placed on bridging, or on purlins or girts that have not been fully bolted into position and with the correct bridging installed. Bolts must be the correct size and grade, all progressively fully tightened during installation.

Laps must be bolted in the outer web hole closest to the sheeting , and the inner flange holes provided. Last but not least, you have to choose the best supplier for you to order purlin. Other than reputation , there are some elements that make the best purlin supplier. Production capacity of the manufacturer decides how long it takes you to receive the purlin. The higher the production capacity is, the shorter time you have to wait. It depends on their factory size and technology they applied.

In general, big manufacturer have higher production capacity. The production is recommended to be closed from raw material to final product. If so, the manufacturer can completely manage the quality of the purlin. If they are not steelmakers and need other steel supplier, they cannot be sure about the exact material and production process. What will happen if your purlin are rusty after 3 months being used and when you contact your supplier, they blame it for the steelmaker.

Each production stage should use separate and modern production techniques.