3. We are the Main Contractor, we have been awarded by the Employer to construct a Tall Commercial Building under the “Design & Build” Contract, where the Employer would only provide the Architectural design and all the other items including Structural Design are going to be performed by us. However, the Professional Engineer (PE) that we engaged for the Structural Design refuse to oversee the design and construction of Glass Curtain Walls.
Our Answer to you:
I do not understand why the PE that you engaged refused to oversee the Glass Curtain Walls work.
What I can advise is that, the structural design of any tall building normally integrates closely with the design and installation of curtain walls, especially when it is “Glass Curtain Wall”. The reason is that, whenever curtain walls are used in any tall building design, the lateral deflection and differential deflection between each storey would become major considerations.
Each curtain wall system is unique and has their own limitation concerning deflection characteristics. For example, a Metal Curtain Wall System would definitely be more flexible and have higher “allowable differential deflection limits” compare a Glass Curtain Wall Panel of the same size, because “Glass” material behaves badly in bending and would break easily.
Any Engineer who is involved in the Structural design of a building cladded with curtain wall, would need to seriously take into consideration the “Deflection Limits” and “Differential Deflection Limits” of these curtain walls to ensure that that the structure that he designed does not deflect more that such limits, so as not to cause any “distress” or possible failure of the curtain wall to be installed, normally after the completion of structural works.
In order to limit the lateral deflection of the designed building, a responsible Structural Engineer would need to increase the rigidity of the Structure against lateral loads, including wind loads. This is how he normally does:
A. Design the Columns in that building to resist lateral loads;
B. Include in his design, Braced frames, Rigid Frames, Shear Walls, and other Interaction System to take the lateral loadings.
C. Use Tubular Frames, Tube within a Tube, and Combination;
D. Use one or combination of any of the above.
Wind loads on buildings are established in all building codes. Depending on the experience of the design engineer and on the building locations, height, shape and exposure, and in certain cases on its mass and stiffness (damping). Wind tunnel testing to determine the adequacy of code winds may be necessary. This is a complex subject, which I would not elaborate further here.
The purpose of the wind-bracing system in a multi-storey framework is to dissipate the wind shear throughout the framework and ultimately to the foundations. The usual framework consists of a series of wind bents placed in a more or less symmetrical patterns with floors acting as stiff horizontal girders to distribute the storey shears to each bent.
There is no preferable form of wind bracing. Each framework must be evaluated with respect to the architectural, mechanical, and structural problems to be resolved.
From what I explained above, you would understand that you need to increase the rigidity of the structure, so that it would not deflect excessively to cater for the Curtain Wall System deflection limitations. Thus you would need a proper lateral loading bracing system mentioned above. That is way the Structural Design and the Cladding Design are so closely connected, that you just can’t perform one without taking the other into serious consideration.
To solve your problem, you may need to take the following steps:
A. Change your Structural PE or
B. To have another in-house PE to help you to coordinate all the related works. If he/she is good and experienced, he/she should be able to help you not only the above mentioned work, but also all related architectural, mechanical and electrical items in your project.
Er. Goh Cheow Leng Maria
First drafted on 10 September 2008.