GTE Corporate Headquarters
Las Colinas, Texas
4 Stories, 1,200,000 Sq. Ft.
$150 M

Architect: HKS

This was one of the most unique and memorable projects of my 40 year career as a structural engineer in Dallas, Texas.  From the very beginning it had all the challenges a structural engineer may be asked to address in one project.

Fast Track Construction
First, it was a “fast track” project with one of the most rapid design and build schedules we had ever encountered.  The project which consisted of 1,200,000 sq. ft. of office space to be constructed on an underground loading dock and 2,900 car parking garage was to be constructed in 22 months plus 2 months move in time.

The entire design and construction team performed at the highest level of professionalism and competence so we can’t take sole credit for making this project a success.  However, I do believe our experience with fast tracking complex major projects gave us the ability to contribute at the high level that this project required.

One of the hidden penalties that an owner often pays on a fast track project is in oversized foundations and other structural elements that had to be conservatively designed by the structural engineer in order to perform his design work within the schedule.  We wanted to make sure this didn’t happen on this project and felt that our experience would allow us to produce an economical structure while, at the same time meet the schedule.

Value Engineering Continued in Spite of the Fast Track Schedule
A. Pier Load Test.  When we received the soil report, we were disappointed in the low allowable bearing values that were assigned to the shale bearing strata.  We had very large column loads and hundreds of piers to construct.  The foundation was going to be extremely  expensive.  We were not satisfied with proceeding on this basis in spite of the tight schedule  pressure we were under.  After considerable discussion with the soils engineer, we proposed  to proceed with a full scale load test with appropriate strain gages etc. to be able to accurately evaluate the load carrying capacity of the shale.

We were not assured that the load test would produce higher allowable values, and therefore, the cost to the owner for the load test was a risk.  But, they agreed that the potential savings was worth the gamble.

This test was performed on a full sized pier on the site as our engineers proceeded running   down the column loads in the office. Our plan was to have all of the pier loads calculated and be ready to size the piers as soon as the results of the load test were known.

The results were very favorable and the soil engineer gave us higher bearing values to use in  our pier design.  Even after subtracting the cost of the load test, over $200,000.00 was eliminated from the cost of the foundations and we stayed on the fast track schedule to deliver  pier drawings to the contractor.

It would have been very easy to proceed with the values in the soil report.  This is the normal  approach even on a conventional project.  But, we didn’t let the fast track pressure deter us from  performing our services in a high professional manner.

B. 50’ x 50’ Bay.  This was an unusually large bay for an office building and the most economical framing system was not readily evident.  In addition to the large bays, we needed to construct the building on top of a 3-4 level below level garage.

First, we wanted to avoid costly transfer girders above the garage.  We worked very closely  with the architect to identify a column layout in the garage that worked with the column   layout in the office building above and ultimately only had a very few number of transfer girders.

Second, we were to construct 1,200,000 sq. ft. of office building and wanted to find the   most economical framing system for the given program. We value engineered various steel and concrete systems and came to the following conclusion:

1) Build the below grade parking garage with post tensioned concrete construction.  The span in one direction was 50’-0” (matched the spans above) and in the other direction alternated between 20’ and 30’ to work with the parking layout and the 50’ span above.

2) Structural steel was chosen for the office building.  Structural steel was faster to construct since fabrication of steel could occur during construction of the garage. Also, the depth of the ceiling space could be reduced by threading the ducts through the steel beams. This allowed us to construct a 50’ x 50’ column spacing 15’ floor to floor height and a 11’ - 10” ceiling height.

Considerable coordination time with the mechanical engineer was required on our part to identify the duct penetrations in the steel.  In spite of the fast track schedule, this extra effort was undertaken to accomplish the most economical structural frame for this project.

3) New LRFD Structural Steel Design Guidelines.  The American Institute of Steel Construction had just released a new ultimate strength design specification.  This new specification would allow us to save 1.6 tons of steel per bay and $200,000.00 on the overall frame cost.  It was new to us and our computer programs were not set up to use this new approach.  But, the savings were too great to ignore, so we proceeded with LRFD, met the schedule and saved $200,000.00.

4) Roof Design for Acoustical Criteria.  We were well into the project when it dawned on us that the light steel and metal deck roof may not provide the desired acoustical properties to reduce airborne noises considering how close the building is to DFW Airport.  An acoustical study was made which confirmed the need to pour a concrete slab on the roof to provide mass to dampen airborne noises.  We revised our roof design to accommodate this new criteria and remained on schedule in the process.

Expansive Clay Site
This site consists of the normal expansive clays and shales found in the Las Colinas area.  Our years of experience working in the Las Colinas clays since the development began in the early 1970’s allowed us to quickly address the issues with the soils engineer and generate successful structural solutions for slab-on-grade construction in the garage, properly designed piers, and appropriate slope protection during construction.

We had one very interesting design issue in the expansive clays that was unique to this project.  A normal technique for reducing pressures on basement walls due to expansive clay is to backfill against the walls with a low P.I. (sandy) material with a drain tile and sump pump at the bottoms. We were well into the project when we realized this system of backfill against walls adjacent to the lakes to be constructed would produce a draining effect on the lakes.  So we revised and re-issued the design in the lake areas to strengthen the basement walls to resist pressures from the expansive clays and deleted the low P.I. (sandy) material under the lakes.

Construction Quality
Another hidden premium owners often pay for fast track construction is low quality construction.  Things like all of the reinforcing steel not being in place when the concrete is poured, cambers in the steel beams not checked before the slab is poured and so on.  All these things become sacrificed in the interest of the schedule.

This didn’t happen on this project.  We all met early in the project with the contractor’s structural job contractors and outlined a quality control program that we would all follow.  I believe as complex as the post-tensioned concrete underground garage structure, that this was one of the best constructed structures I’ve seen.  All of the test reports on both the concrete and the tendon stressing were excellent.  The structural steel job was excellent.  The contractor’s commitment to quality, in spite of the schedule, was the best I’ve seen.

From a structural point of view, the owner received a high quality structure in spite of the schedule.