IEM PI Section A – Design experience related 3

(For PI section A, candidate will have to write an essay, which the question was earlier prepared by interviewers based on candidate’s Report on Training and Practical Experience. The following were predicted questions, by Mr. BAY based on his submitted report to principal interview and his trial exercise prior to sitting of PI.)

Design Experience Related Question

What are the investigations needed for additional construction onto as-built structure? What are design concerns and practices should be taken?

Introduction

Additional construction to as-built and existing structure is challenging work and need due care and examination to the existing structure. It is especially true when the new or additional structure is proposed on top of existing one compared to extension at adjacent area of the existing one.

The following are some aspects that require engineer to study during the design process.

1)      As-built drawings

Examination to as-built drawing is essential. The purpose is to know the as-built structural framing such the beam arrangement and column layout. Their size and rebar details are also needed.

The examination of as-built drawings enable design engineer to produce early new structural framing on top of existing ones. With reference to as-built drawings, engineer could only decide when the new columns and supports shall be placed.

2)      Design load of as-built structure

The design report and design load of as-built structure is essential to facilitate design work of the additional structure. It is because total weight of the new items shall not exceed the supporting capacity of the as-built structure.

If this information is not available especially with existing structure which is built some time ago, the design engineer will have to be more conservative in assessing the structural capacity of the as-built and probably to do another thorough modeling and analysis together with the additional items.

3)      Structural system

Upon finish of table study on as-built drawing and design report, design engineer will have to consider the appropriate structural system such reinforced concrete system, structural steel or others.

For the project Aeon Shopping Mall Kulaijaya, which I have done and designed the new cinema platform onto as-built second floor rc system, I have decided to adopt structural steel with composite deck system. It is because there are plenty stepping platforms (different level) for cinema seats. If structural concrete system is adopted, there will be plenty of formwork needed, difficult to demobilize the formwork, the concrete member are also much heavier compared to structural steel.

4)      Field study and verification 

Field study of the as-built structure could help design engineer in their design too. It is because design engineer could feel better the clearance and possible discussion with contractor and fabricator regard to construction access, available equipment and machine for lifting of structural member within enclosed space.

By field study and discussion with contractor to know their construction management, design engineer could design better structural system such as beam or truss and possible the joint location to facilitate transportation and movement within enclosed space.

Conclusion

Unlike designing a total new structure, which design engineers to prepare the design based on requirement, design engineer will have to consider the as-built structural framing supporting new structure. New and additional structure shall not impair and damage the as-built one. Alteration and modification to as-built structure, if deemed unavoidable, careful study and proper detailing are needed.