Mixed Apartment Complex
Small City, PA
Antonio Thomas │ Structural
Adviser │ Dr. Thomas Boothby, P.E., R.A.
Proposal Draft
Proposal Revised 1/18/19
Structural Depth
Using conventional structural systems, it is difficult many floors in this mixed-use apartment building with a 100’ height restriction. The building consists of large bays that span approximately 25’ in at least one direction. Not only do conventional structural systems pose a problem to the height limit, there are not many structural systems capable of supporting the required loading over such a span without having to resort to deep floor depths. The current system in place is a Delta Beam – hollow core plank configuration that certainly gets the job done, but is an international product that requires a second structural engineering firm to work the job. This provides additional costs to the owner and can slow the process of construction due to shipping the materials.
A possible alternative to the presented challenge is using a podium structural system with light gauge steel framing above the podium instead of wood members. There are floor joist members that are able to span around 25’, the current typical span, with depths less than 12”, the typical depth with the current system. This will help reduce loading on the gravity system that allows for these spans without the need for thicker floor depths. The lighter weight of the light gauge steel will also allow for quick construction due to materials, tools, and equipment being able to be carried by hand. With the column layout remaining similar to the current system, the load bearing walls will primarily focus on resisting lateral loads. When the structure reaches the podium level, a transfer slab will be investigated in order for the loading to move towards the concrete load bearing walls of the parking garage stories. Podium style structures are typically made of wood above the podium levels. Light gauge steel was decided to be used in place of the wood because more stories should be attainable due to the fireproofing of steel and steel requiring less members to achieve the same strength. It allows quicker and cheaper construction, putting that saved amount towards additional stories.
Acoustical Breadth
Although the interior partitions will remain the same, moving from a concrete plank flooring system to light gauge steel joists may cause more sound between units. Due to a concrete flooring system being more solid, it is able to dampen sound better than the steel joists. An investigation to make analyze the acoustics with the alternative system in place will be conducted to see if sound may pose a significant issue for occupants. If there is significant change to the acoustics, research of a cost-effective solution will occur. Possible solutions are to provide a flooring underlayment, joist isolators, or a proper floor finish (e.g. hardwood, carpet, engineering flooring).
Construction Management Breadth
A cost and scheduling comparison between the existing system and alternative system will be under investigation. The use of a podium structural system that utilizes light gauge steel framing above the podium will be lighter than the existing causing quicker construction. This is due to not having to rely on heavy tools and equipment to carry the components. Also, Delta Beams require a concrete infill in which shoring is necessary for the curing process. With the alternative system, the use of concrete at stories above the podium level will not be needed; therefore, no time for curing will be placed in the scheduling, reducing the time of construction further.