Noteworthy

Malone Cliff View Residence Soars over Dallas

By Thomas W. Taylor, P.E., Stephen Price, P.E., Lee Christian, P.E. and Craig Rios, P.E.

Datum Engineers, Inc. was an Outstanding Award Winner for the Malone Cliff View Residence project in the 2015 NCSEA Annual Excellence in Structural Engineering awards program (Category – New Buildings under $10M).

This unique residence sits on the top of a bluff which originally was a 60-foot deep landfill of trash, tires, and more. The Architects design intent for the residence created three specific amazing views of the Dallas skyline. Parts of the house and balconies soar 17 feet out over the cliff with thin post-tensioned concrete slabs. These soaring cantilever floors accentuate the view in a dramatic way. The architectural centerpiece of the interior of the house is a two story spiraling steel stair which is also a part of the architectural appeal of the exterior of the house, as it can be seen through the glass window at the front entrance. The site conditions, and desired architectural and functional expression, created numerous structural challenges not often found in residential construction. Four of these challenges were the major influence on the structural design concept. First, the trash landfill created the need for deep vertical piers through the unstable fill to support the load of the residence, and battered piers to resist the horizontal sliding forces created by the bluff. A key to the success of the foundation was working closely with the contractor to identify sizes and location of both battered and vertical piers that could be accessed with special equipment. Finding the type of equipment that the contractor could drive out onto the bluff, and then designing the foundation around this restriction, was a major challenge. This was a difficult but successfully completed challenge with close teamwork between the structural engineer and the contractor. Second, the only reasonable structural system that would accomplish the architect’s vision was a post-tensioned cast-in-place concrete slab. The architectural vision deserved thin concrete slabs. But, the thin slabs had to cantilever 17 feet. An added complication was that the cantilevered slabs needed to be supported on thin concrete slab bands that were formed flush to the bottom of the slab. Both the cantilevers and the slab bands were integrated into a 10-inch concrete slab with no drop beams. The concrete slab design and construction was further complicated at the roof, which was formed as a slight hyperbolic parabola. Engineering analysis of the post-tensioned cantilever slabs to prevent differential deflections that could lead to glass breakage at the ends of the cantilevers was a major tedious engineering effort. Deflections at the tips of the cantilevers varied depending on the length of the cantilever slab and the length of the supporting slab band. This required a thorough analysis of deflections at the tip of the cantilever and along the slab band to hold tight deflections and coordinate with the architect’s window wall details. No drop beams were used to stiffen the floor, in order to accommodate the air conditioning ducts and light fixtures in the low floor to floor height. Lee Christian P.E. used ADAPT-PT and ADAPT-Floor Pro software to analyze the slabs. Final measurements of deflections after construction were compatible with the calculations, and a successful solution to the architectural vision was accomplished. Third, the two story architectural centerpiece stair was constructed of a single center-spiraling welded steel box beam that was only connected at each floor access point. Two cantilever steel cross plates, cut into the wood treads, were welded to the spiraling steel box beam, to support each tread. Structural considerations of a spiraling box beam and control of vibration characteristics, created a major analytical challenge to create an ultimately simple appearing, but structurally successful, architectural centerpiece. Craig Rios P.E. used SAP2000 to calculate the stresses, deflections and vibrations, and created a successful structural solution for the architectural centerpiece expression. Fourth, originally there was no apparent method to support the circular steel roof over the stair without adding bulky columns behind the window wall. The ultimate solution to this structural challenge was to integrate small structural steel supporting tube columns into the glass exterior wall, eliminating any appearance of structural columns adjacent to the window wall. The steel tubes became the window mullions in addition to supporting the steel roof. This wall of steel and glass was meticulously detailed, and kept as thin and lightweight as possible. This allowed for views of the centerpiece from the outside, let light in, and created a dramatic architectural entry to the residence. A strong aspect of this award winning residence is its integration into the environment. The architectural vision, in large part, was made possible by the structural concept. A beautiful and dramatic home now sits on a bluff that was once a trash landfill.▪

Thomas Taylor is Principal Design Engineer of Datum Engineers. Thomas can be reached at thomas@datumengineers.com. Stephen Price is the Technical Director and a Principal of Datum Engineers. He functioned as the project manager on this project. Stephen can be reached at stephen@datumengineers.com. Lee Christian is a Senior Associate at Datum and performed the concrete design on this project. Lee can be reached at lee@datumengineers.com. Craig Rios is President of Datum|Rios in San Antonio, Texas and designed the spiral stair for this project. Craig can be reached at c.rios@datumrios.com.

ASSOC I A T I O N S NATIONAL COUNCI L

NCSEA News

Structural Engineering Education: Preparing for Our Future Engineers

During a spontaneous discussion at a National Council of Structural Engineers Associations (NCSEA) Annual Conference over 13 years ago, a group of practitioners and educators shared their concerns over the increasing lack of technical knowledge exhibited by recent college graduates. This informal gathering launched the formation of the NCSEA Basic Education Committee (BEC). The NCSEA BEC has expanded its efforts from its early beginnings to address different challenges that face the structural engineering profession. The BEC along with other NCSEA efforts seek to maintain and strengthen the process of preparing structural engineering students to practice structural engineering as licensed professional engineers. The process of preparing students to become competent licensed professional engineers focuses on three main elements: education, examination, and experience. The BEC is committed to sustaining and improving a future structural engineer’s educational experience, upholding a strong examination process, and encouraging licensed professional engineers to provide structural engineering students with an opportunity to receive a successful mentorship experience. A sound educational experience is instrumental in the development of a competent licensed professional engineer. The recommended NCSEA Structural Engineering Curriculum encourages structural engineering students to receive instruction in the following subjects: structural analysis, matrix methods, steel design, concrete design, timber design, masonry design, dynamic behavior of structures, foundation design / soil mechanics, and technical writing. These subjects are further defined as twelve recommended courses. Each recommended course suggests topics and objectives that are encouraged to be covered as part of the curriculum. The BEC has begun the arduous process of reviewing each recommended course’s suggested topics and objectives. The recommended curriculum, available on the committee’s page on the NCSEA website, was one of the first tasks completed by the BEC in an effort to improve the quality of structural engineering education. This month the BEC is distributing the 2016 NCSEA Structural Engineering Curriculum survey, a triennial comparison of the recommended NCSEA Structural Engineering Curriculum, to college professors at nearly 300 engineering colleges across the country. Participation by engineering colleges is important for the survey’s success, and we encourage interested NCSEA member organizations to contact the BEC to determine how they may assist with increasing the survey response. The results of the survey will be published in the August 2016 Issue of STRUCTURE magazine and will be posted on the NCSEA website later this year. Over the years, the BEC has solicited and received feedback from practicing structural engineers and educators concerning the recommended NCSEA

The BEC is committed to sustaining and improving a future structural engineer’s educational experience, upholding a strong examination process, and encouraging licensed professional engineers to provide structural engineering students with an opportunity to receive a successful mentorship experience.

Structural Engineering Curriculum by (i) regularly publishing education articles in STRUCTURE magazine, (ii) engaging other organizations directly (AISC Partner’s in Education, ACI’s Faculty Network, AWC, etc.), and (iii) holding numerous informal conversations with engaged NCSEA members. The BEC is currently preparing a formal practitioner survey of the recommended curriculum, to be distributed later this year to all NCSEA members. The results of the practitioner survey will serve as a guide for the BEC to review and, if necessary, the BEC will revise the recommended curriculum to ensure that the curriculum continues to meet the demands of the structural engineering profession. The BEC continues to work with the Structural Engineering Certification Board (SECB) in an effort to develop and implement an SECB Education Certificate program at interested colleges. The SECB Education Certificate is a transportable document that will guide collegiate choices to ensure alignment between academic and professional goals. The education certificate would also serve as a means to identify individuals that have met the educational requirements necessary for SECB certification. The BEC believes it is critical that the profession recruits talented high school and collegiate students to ensure future successes. The BEC has created an NCSEA High School Outreach Guide to aid member organizations in creating a successful high school outreach program. The BEC is also in the process of developing an NCSEA College Outreach Program titled “Become a Structural Engineer” that includes a trifold brochure and slide presentation. The NCSEA High School Outreach Guide and “Become a Structural Engineer” brochure are now available for download from the NCSEA website, after login, under NCSEA Committee Documents and Resources. The “Become a Structural Engineer” slide presentation will be available later this year. The BEC SE Connect group seeks to increase the effectiveness of its efforts by partnering with similar member organization committees or with interested members acting on their member organizations’ behalf. The BEC gathered potential contacts to assist with the SE Connect Group at the 2015 NCSEA Summit Annual Meeting and is looking for additional assistance. Please contact Brent Perkins, NCSEA BEC Chair at bperkins@dwase.com if you are interested in participating in the SE Connect Group.

Brent Perkins, P.E., S.E. Basic Education Committee Chair