A new Roof-Top units is added with previous Steel Roof Structure

A right amount of experience is needed to know the exact problem of existing Steel roof structure before adding a new Roof top unit with it as the work needs experienced methods to do.

Often contractors are asked to calculate a previous steel roof structure to establish if it can support new roof top units or not. Often tenants remodel commercial spaces for their needs and also sometime new air make-up units, exhaust fans and HVAC units need to add.

What is Roof Top Unit: A packaged rooftop unit or RTU is a kind of HVAC system that has all the components needed to supply conditioned air in one brief unit. Packaged rooftop units are naturally found in light and large commercial applications. They are very famous in the construction industry with retail and industrial properties.

The Roof-top Unit or Roof Top Air Handling Unit supplies Heating, Ventilation, and Air Conditioning (HVAC) to the space below. Air duct Smoke Detectors or Duct Detectors can be inside the Roof Top Unit or in the air ducts below it.

In this article we are going to show evaluations of two commercial spaces for new rooftop units; where one space was adding a commercial kitchen and needed new exhaust fans and air make-up unit while the other needed new cooling units to reverse all the extra heat that was coming.

New roof top units can be large and heavy and generally affect the existing roof structure; sp at first the existing roof structure is examined to know the size, space and span of the joists, location of bearing walls and girders and location of previous roof top units. Generally a typical commercial roof structure is constructed with steel bar joists which are mainly tagged by the manufacturer like Vulcraft who keep records of joists’ type to use in the projects. Next all the accurate measurements of the top and bottom flanges, the web members and the length of the joist has taken; besides all this contractors have to observe other parameters to make sure all new and previous load can be transferred to the supporting structure in the right way.

After that the ability of from the manufacturer is determined and/or is modeled as per its section properties which help the contractors to calculate the load carrying capacity of the steel joist. As previous joists don’t have a lot of extra load carrying capacity so they can be strengthened by welding steel rods and plates to the flanges. But it is always best to locate a new unit away from previous units and near the previous bearing wall or girder which will limit the amount of new load on the previous joints. So basically it is mandatory to examine a previous structure to know its strength and capacity and qualifying it accordingly the new one as it creates a good understanding of structural design as well as a wealth of knowledge of building construction.



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Published By
Rajib Dey
www.constructioncost.co
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Illustration of stress-strain curve for concrete and steel

This construction video tutorial will teach you the detailed process for creating the design of stress-strain curve of concrete and steel by adhering to the IS 456:2000. Limit State Method is used here for these curves.

As the tensile strength of concrete as compared to compressive strength is very week, it can only withstand compressive stress. Alternatively, the tensile strength of steel is very strong and it can withstand both tensile and compressive strength.

While going to design a structure located in costal area and as per IS code the minimum grade of concrete for this structure should be M30 and concrete can’t be used below this grade. It is known that 30th characteristic strength of concrete cube of size 150 mm at 28 days. The characteristic strength is represented with the symbol as fck.

The stress-strain curve for hardened cement paste is nearly linear. The aggregate is more stiff as compared to the cement paste and will consequently deform less (i.e. contain a lower strain) under the similar applied stress.

The stress strain curve of concrete remains among those of the aggregate and the cement paste. But this alliance is non-linear over the most of the range. This non-linear behavior occurs because of formation of micro-cracks for the following reasons :-

(i) At the interface among aggregate particles and cement paste due to the differential movement among the two phases, and
(ii) Inside the cement paste itself.

These cracks are developed owing to variations in temperature and moisture and the application of load.

To learn the detailed process, watch the following video tutorial.

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Published By
Rajib Dey
www.constructioncost.co

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Why Steel Roof Truss Is Better Than Timber Truss?

A truss is formed with an assembly of inflexible & elastic members which are connected as the triangles to perform like a beam. The tensile stress of mild steel is secure for working and it is approx. 20 times as compared to structural timber. Therefore, steel trusses are considered as cost-effective, particularly for largest extents. The angles are treated as the most vital elements for steel roof truss among different shapes of steel sections due to their capability to withstand both compressive and tensile stresses in an effective manner. The supplementary angles are created inexpensively as well as connected without any difficulty.

Benefits of steel roof truss as compared to timber truss are presented below:

1. Steel trusses last long as compared to timber trusses.

2. Steel sections that develop the truss are lightweight and are constructed in any preferred pattern to match the requirement of any architectural work.

3. As it is made with steel, the material is not damaged by white ants or other insects.

4. Steel trusses contain strong fire-resisting capacity as compared to timber trusses.

5. As there are no span limitations with steel trusses, they can be utilized for industrial buildings and various other structures where large areas can be covered devoid of any obstructions which may occur to columns etc.

6. The sections which develop a steel truss can be smoothly transported.

7. The sections are acquired in any preferred form or length to match the requirements and less wastage of the material occurs in cutting etc.

8. Due to their trouble-free erection methods, the advancement of roofing work with steel trusses can be done rapidly.

Article Source : www.dailycivil.com

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Published By

Rajib Dey

www.constructioncost.co

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