Traci Peterson Option: Structural Faculty Consultant: Memari. Executive Summary

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1 1 Traci Peterson Option: Structural Faculty Consultant: Memari The Del Monte Center at The North Shore Pittsburgh, PA Thesis Proposal Date of Submission: 12/10/04 Executive Summary Currently under construction on Pittsburgh s North Shore, The Del Monte Center is a 285,000 square foot, six-story office complex including 41,000 square feet of retail and restaurant space on the lower floors. The building is a steel braced-frame structure, with composite floor systems. The façade is comprised of stud and metal panels with brick and stone veneers scattered throughout. It was very important to the architect to have large open bays to accommodate unobstructed windows. In order to accomplish this, a system of improvised knee braces (in the shape of narrow V s) was created for the exterior bays in the long direction of the building. While these braces serve the architect very well, they are rather inefficient structurally. For the depth work of my thesis, I am proposing to study several alternative bracing systems. I plan to redesign the bracing in the long direction using moment connections, since the narrow V s are very close to moment connections as it is. I also plan to redesign those braces as full bay bracing, the implication of which will be either exposed bracing or opaque bays. Both of these alternatives will be evaluated in terms of economy in steel design, and compared to the existing system. For the breadth work of my thesis, I will be analyzing the implications of the alternative systems on the architecture of the building. Also, for the full bay bracing alternative, I will be analyzing the implications of having opaque bays on the lighting and mechanical systems. The following sections are included in the thesis proposal: Background information about the Del Monte Center Description of the existing lateral system design Descriptions of two proposed alternative bracing systems Description of the methods to be used to analyze the redesigns Description of the tasks and tools which will be required to analyze the redesigns Proposed schedule to be followed in order to complete the analyses

2 2 Background Construction of The Del Monte Center began on Pittsburgh s North Shore on June 10, 2004 and is expected to be completed in late The office complex is six stories plus two rooftop mechanical penthouses, totaling a height of just over 100 feet. The lower floors include 41,000 square feet of retail and restaurant space, while Del Monte Foods is the major tenant of the upper floors. The building is comprised of two distinct parts, called Units A and B, with a total square footage of 285,000. Units A and B are approximately rectangular and are connected on the fourth through sixth floors by continuous slab floors. Underneath the connecting bridge is a landscaped pedestrian court, which serves as a means of egress through the building without having to enter inside. A key plan of the footprint of the building is shown below: a b n The façade is comprised of stud and metal panels with brick and stone veneers scattered throughout, with the exception of the curved section of the west end of the building, which is entirely glass. The base is a sandy color and all of the glass is gray. The brickwork is predominantly light red with yellow accent strips, and was designed to compliment surrounding buildings on The North Shore. There are large bays of unobstructed windows all along each side of the building in the long direction. The typical floor systems are lightweight concrete slabs on composite steel deck. These composite slabs are supported by a composite beam system. The slab-on-grade foundation is founded on auger cast piles. Typical exterior wall construction behind face brick or cast stone masonry units is composed of an airspace, asphalt felt, gypsum sheathing, metal studs with fiberglass batt insulation, vapor barrier, and gypsum wall board. Wall construction behind fiber reinforced plastic panels is the same, minus the airspace. The framing of the steel structure does not vary significantly from floor to floor, and the bays in both units are relatively consistent, although no two are identical. Typical beam spans are feet and typical girder spans range from 28-8 to The columns are continuous. Elevators and stairs are located in the center of Unit A and on the east side of Unit B, and clustered around them

3 3 on each floor are mechanical and electrical rooms. These areas, along with the connecting bridge between the units, account for most of the departures from the typical bays. The lateral system is composed of braced frames. In the north-south direction, the braces are mostly inverted K-braces, also known as chevrons. In the east-west direction, they are simple noneccentric knee braces. The braces are connected to the frames with pin connections. The girders are connected to the columns with shear connections, which can also be modeled as pins. The diagrams shown below outline the location and shape of the braces:

4 4 Existing Lateral System It was very important to the architect to have large open bays to accommodate unobstructed windows. In order to accomplish this, the engineers created a system of improvised knee braces (in the shape of narrow V s) for the exterior bays in the long direction of the building (see graphic to the right). While these braces serve the architect very well, they are rather inefficient structurally. Proposed Alternative Bracing Systems For the depth work of my thesis, I will be studying two alternative bracing systems, with an overall theme of economy in steel design. I will be considering only the exterior lateral force resisting bays in the long direction, where the inefficient narrow V braces are currently in place. Alternative #1: Because the geometry of the narrow V braces causes them to act very similarly to moment connections, the first redesign that I analyze will consist of changing the connections in the aforementioned bays to moment connections. This will eliminate all of the diagonal bracing members. However, moment connections are more expensive than the shear connections that are present in the existing design. Alternative #2: For the purposes of my thesis, I will be assuming that I am not subject to the same architectural constraints that the engineers were who designed the building. With that said, the second alternative bracing system that I analyze will consist of full bay bracing in the bays in question. The bracing that I intend to analyze will be in the shape of inverted K s, similar to the bracing in the short direction (see graphic at right). This is a more efficient and cost effective design. However, the implication of this design is that there will be either exposed bracing or opaque bays. Changing the nature of these bays affects many aspects of the overall building design, not just the structural system. These aspects will constitute the breadth work of my thesis. For instance, the architecture of the building will be radically altered. Also, if the bays are made opaque, the lighting and mechanical systems of the building will be affected due to the reduced amount of light and heat entering the building through the façade..

5 Methods To Be Used For Redesign The redesigns that I am proposing will involve the use of a variety of different methods in order to complete. I will analyze both alternative bracing systems using the loads calculated in Technical Report 1 with the loading conditions analyzed in Technical Report 3. The loads on the individual framing members will be determined by modeling the frames in STAAD. Once these loads are known, the members and connections can be designed using the AISC LRFD manual. The cost of the structural steel used for each alternative system, as well as the existing system, can be obtained through AISC. The cost to fabricate the connections can be obtained from a steel fabricator. Labor costs can be found using R.S. Means. The impact that exposed bracing or opaque bays will have on the architecture of the building will be analyzed by creating renderings of the redesigned building while experimenting with a variety of different building envelope materials. Leaving the bracing exposed could create an interesting architectural opportunity to tie together the steel skeleton design of the Del Monte Center with the steel skeletons of the surrounding bridges as well as the exposed structural nature of the two nearby ballparks. This will change the architectural intent of the building from complimenting the surrounding contemporary buildings to complimenting the bridges and ballparks, which in my opinion, better captures the spirit of Pittsburgh. 5 To analyze the implications of opaque bays, I will calculate the decrease in the amount of lumens entering through the building s façade due to the decrease in area for light to travel through. This amount will then be used to determine the impact on the building s lighting system. In the same sense, the change in the building s envelope will require that new loading conditions with regard to the mechanical system be calculated. These loads will then be compared to the existing loads. The overall effect on the mechanical system will be found, and the necessary changes in duct size will be determined.

6 6 Tasks and Tools To Be Used For Redesign Task 1. Redesign bays using moment connections A. Make any necessary changes to the loads calculated in Technical Report 1 B. Determine how the loads will be distributed to the redesigned bays C. Model the bays in STAAD, using moment connections instead of braces D. In STAAD, apply the loads to the bays and determine the critical loading condition E. Use STAAD to find the loads on the individual members F. Using the AISC LRFD manual, size the members and design the connections Task 2. Redesign the bays using full lateral bracing A. Model the bays in STAAD, using full lateral bracing B. In STAAD, apply the loading condition determined in Task 1 to the bays C. Use STAAD to find the loads on the individual members D. Using the AISC LRFD manual, size the members and design the connections Task 3. Analyze costs of materials and fabrication- using information from steel fabricator and AISC A. Determine cost of existing bays B. Determine cost of bays with moment connections C. Determine cost of bays with full lateral bracing Task 4. Analyze erection costs using R.S. Means A. Determine labor cost for existing bays B. Determine labor cost for bays with moment connections C. Determine labor cost for bays with full lateral bracing Task 5. Study impact of redesign on building s architecture using AutoCAD A. Create a rendering of the building with full lateral bracing exposed B. Create renderings of the building with opaque bays, experimenting with different building envelope materials Task 6. Study impact of redesign on lighting system A. Calculate the amount of lumens entering through the existing façade B. Calculate the amount of lumens entering through a façade with opaque bays

7 7 Task 7. Study impact of redesign on mechanical system A. Calculate the change in loads caused by the redesigned building envelope B. Make necessary changes to mechanical equipment Task 8. Prepare final presentation using Microsoft PowerPoint Proposed Schedule week tasks to be accomplished 10 Jan task 1 17 Jan task 1 24 Jan task 2 31 Jan task 3 7 Feb task 3 14 Feb task 4 21 Feb task 4 28 Feb task 5 7 Mar Spring Break 14 Mar task 6 21 Mar task 7 28 Mar task 7 4 Apr task 8 11 Apr Presentation