PROPOSAL
Executive Summary
The West Tower of the West Rosslyn Area Planning Study (WRAPS) is a mixed-use facility functioning as both a retail/commercial space and 331 units of one to two-bedroom apartments with a supporting tenant amenity space located within Arlington County, VA. The Public-Private venture between Arlington Country officials and the primary land developer, Penzance, has resulted in total redevelopment of the West Rosslyn area resulting specifically in the design the 413,810 square-foot and 240-foot-tall west tower.
The typical structural gravity system is composed of an 8” post-tensioned concrete slab with additional reinforcement provided at the varying slab edge floor to floor which contribute to the architectural exterior of the building. The slab is supported by 35 reinforced concrete columns varying in size and shape dependent on location in the building, additional reinforcement is also provided over each column.
The lateral structural system included in the building is a combination of two vertical shear cores and a single shear wall that create a center of rigidity at roughly the geometric center of the building. The shear cores are 16” reinforced concrete with continuous walls and returns in the N-S and E-W direction of the building. The single shear wall runs in the E-W direction at the North end of the building.
As a design alternative to the original structural system, a partial prestressed concrete slab supported by reinforced concrete columns will be implemented as well as post-tensioned shear walls. An investigation into the benefits and drawbacks of each system based on their cost and schedule implications will be concluded as well as an analysis of the current thermal performance of the existing enclosure.
Depth Topics
Immense care and detail went into the design of a fully post-tensioned slab in the West Rosslyn - West: load balancing, in depth tendon coordination and distribution, determination and remediation of excessive stress regions. Additionally, the effect of architectural features and their consequences such as the thermal bridge create by the continuous slab acting as balconies. An alternative to this full post-tensioned system is a partial prestressed concrete slab. This partially prestressed slab allows for the combination of mild reinforced concrete for strength as well as nominal post-tensioning from stress and crack control.
The structures existing lateral force resisting system in the form of reinforced concrete shear walls with excessive thicknesses act as a fixed building feature limiting architectural fluidity and flexibility. They also require a large amount of mild steel reinforcing to provide the adequate lateral stability determined from wind and seismic loading. Considering these factors, post-tensioned shear walls will be incorporated into the building as the lateral structural system
Breadth Topics
Construction Breadth
While both existing and proposed systems include post-tensioning and mild steel reinforcement, variation in construction means and methods as well as effect on schedule range greatly. For this reason, a cost and constructability analysis will be done on the proposed system based on cut sheets and/or RS Means 2018 to be compared to the provided cost and schedule.
Enclosure Breadth
The buildings existing enclosure is composed of a window wall system with GRFC and back pad with an incorporated rain screen system with window openings being full story heights. The structural proposal will allow for cracking therefore moisture exposure must be minimized. A enclosure analysis of a typical wall assembly will be completed in order to determine locations of excess condensation and implement changes if necessary.
MAE Requirements
Design alternatives will require computer modeling and analysis procedures based on knowledge from AE 530 – Computer Modeling of Building Structures. With the implementation of a unique and progressive lateral system material covered in AE 538 – Earthquake Resistant Design
