As building envelopes become tighter, conditions that compromise the performance of the thermal building envelope become more significant obstacles to the energy efficiency of buildings. Steel, with its high rate of heat conductivity, should be kept out of the building envelope's insulation plane as much as possible. Images from thermal cameras validate the energy loss from steel thermal bridging details. Since energy codes in the U.S. typically don't set limits for thermal steel bridging (as other countries do), it's important to relate this to a building envelope system's R-value. A straightforward way to quantify the reduction in insulation R-value due to the presence of steel elements bridging across the envelope insulation material is presented. Several conditions where thermal bridging can occur are discussed, with suggestions for alternatives to common details that can result in a significant improvement in a building's energy performance. Systems discussed include: cold formed steel stud walls, roof edge conditions, relieving angles, masonry lintels, brick ties, and projecting steel elements.

Hurricanes Katrina and Ike, and to a lesser extent Rita, Ivan and others that have struck the Gulf and Atlantic coasts over the last several years, have caused extensive damage to property. Much of the damage was to the foundation systems or was propagated to the building through poorly performing foundations. From damage investigations after the storms, it almost appears that there is insufficient information for the practicing engineers about how foundations should be designed for these highly vulnerable locations and buildings or the information that is available is being ignored. While the storm surge elevations were extensive for both Hurricanes Katrina and Ike, the performance of building foundations suggests that there is either little design being performed for these foundations or the expected loads on the foundations are not clearly understood by designers. Hurricane Ivan caused damage to shallow building foundations where survival was probably assured had the foundations been deep-driven piles. Many of the building and foundation losses were caused by extensive erosion and scour at the foundation and it is clear this important coastal ‘hazard’ is not being sufficiently accounted for in the design of the foundation. This paper will explore not only some of the foundation damage mechanisms that have occurred along the U.S. coastlines but suggest design approaches that engineers should consider using to help insure greater survival rates of the foundation. The current foundation design guidance that is available for the practitioner from expert coastal construction sources is not sufficient in covering the many important aspects of foundation design that must be considered to resist failing under the extreme loads of coastal storm surge events.

As the importance of protective engineering and multi-hazard mitigation design has been made apparent in recent years, the development of an effective structural protection system that aids in the preservation of life safety during blast events is an important topic of research in structural engineering. Based on prior research, the authors propose the development of a protective jacket consisting of a thick layer of water sandwiched between two thin layers of polyethylene film or a similar polymer membrane, which can be wrapped around or affixed to the vulnerable structural elements.

A simple performance-based test technique was developed for the fire resistance assessment of columns. In this method, the column specimen is tested using a conventional column furnace while it is coupled with a simple analytical model. The simplified model simulates the remainder of the building. The components of interaction between the column specimen and the analytical model are deformations and loads. The new test approach includes the axial load-deformation interaction components. In other words, the axial load of the column specimen is varied according to the structural system response. The simple approach was employed for different building frames and the results were compared and verified with those obtained from an analysis using the SAFIR computer software. This paper provides the theoretical concept and formulation of the simple hybrid test approach. Before putting the model in practice, it will be further verified through a future experimental program.

The Dubai Towers, Dubai is a group of four super-tall towers above a podium surrounded by a manmade lagoon. The towers are arguably the most complicated geometric form proposed for towers of these heights, as they taper, rotate, and curve until they reach their peaks. This paper discusses how the geometry of each tower was subtly reshaped to balance the tower and reduce the internal shear. It also discusses the improvements made to the structural system and the simplifications created for constructability. The revised structure saved 95,000 tonnes of structural steel and 96,000 cubic meters of concrete. The total savings in structural materials alone exceed $600 million U.S. dollars. These significant improvements were only possible through parametric modelling and the application of the custom spreadsheets which allowed numerous iterations in a short duration to optimize both geometries and member sizes. Through a collaborative process, the design team met the challenge of balancing the architectural geometry and structural behaviour, ultimately designing a more efficient group of sculpted towers. The substantial savings and improved constructability transformed the Dubai Towers from an architectural concept into a truly buildable design.

Research and experience of past earthquakes suggest the need for buildings that are less vulnerable to damage and easier to repair after a major earthquake. Our research aims to develop a new structural system that employs controlled frame rocking action and replaceable structural fuses to provide safe and cost effective resistance to earthquakes. The system combines desirable aspects of conventional steel-braced frame systems with energy dissipating shear fuses that are mobilized through rocking action. Vertical post-tensioning is provided to increase overturning resistance and enhance the self-centering characteristics to reduce residual drifts. This is the first of two companion papers to present research findings from a NSF-NEES Small Group Project on this topic. This paper examines the behavior of controlled rocking systems through large (1/2) scale rocking-frame subassembly tests conducted at the University of Illinois. Conducted using quasi-static cyclic and hybrid simulation techniques, the tests demonstrate the viability of the controlled rocking system and provide the basis for establishing design criteria to ensure an appropriate balance of overturning resistance, self-centering capacity, and energy dissipation.

Nature shades the forest floor from the hot summer sun by the intricacies of the tree canopies made from the patterns of leaves. As summer turns to winter the dense patterns open as trees drop their leaves, allowing light to penetrate deep into the forest, and the solar transmittance of the forest changes as a whole. Just as these individual elements within nature work together to change the performance characteristics of larger systems, ETFE foil systems can alter its components configuration to adapt to environmental conditions. ETFE (ethylene tetrafluoroethylene) has been used over the past 25 years for transparent roof and wall systems around the world but the material and technology only made it onto the world stage with the debut of the Allianz Arena for the 2006 World Cup in Germany and with the light filled entrance of the "Water Cube" as the National Swimming Center at the 2008 Beijing Olympics. Now the material with its diverse aesthetic and performance capabilities is being considered the material of choice for traditional skylights, long span structures, and building facades. This paper will explore how this system takes its cue from nature and actively adapts to environmental conditions, producing enlivened and energy efficient building skins.

This paper examines the effect of member self weight on preventing upward buckling of a compression member with horizontal orientation. The unique case of continuous, one-directional bracing with constant brace force but with zero brace stiffness is considered for a practical range of members and applied axial loads. The concept is further explored through an analysis of the stability of an exterior curtain wall that is laterally supported by suspended horizontal tube steel trusses. Under outward wind loads, the compression chord of the truss may be considered adequately braced against upward buckling by its own self-weight.

There is widespread concern among practicing engineers that the clarity and usability of the building codes have radically diminished as the size and complexity of the codes have increased. One tool for assessing the ability of practicing engineers to consistently and reliably implement the code is the use of Trial Design Problems. The Trial Design Problem process consists of (a) developing a common engineering problem, (b) enlisting practicing engineers to complete the engineering problem using the code, (c) evaluating the engineering solutions submitted by practicing engineers, and (d) conveying the results of the problems to the engineering community and code development committees. The Design Practices Committee of the Structural Engineering Institute recently completed a Trial Design Problem related to snow loading per the ASCE 7-05 code and 2006 IBC. The quantitative analysis of the Trial Design Problem solutions indicated that while practicing engineers were able to consistently apply most of the basic ASCE 7 snow load provisions, some concerns with consistent application of the provisions were identified, including: (1) Using ASCE 7-05, approximately 10 percent of the practicing engineers incorrectly identified the roof exposure condition resulting in an under-estimation of the exposure coefficient and the snow load. (2) Using ASCE 7-05, over 20 percent of the solutions did not account for the projection drift load requirements at the parapet of the low roof. (3) Using ASCE 7-05, for those solutions which included a calculation of projection drift at the parapet, the value for the roof length upwind of the parapet in projection drift calculation was not uniformly selected. Based on the results of the quantitative analysis of the Trial Design Problem solutions, recommendations were made for clarifications to the Snow Load provisions of ASCE 7-05.

Since the 1960s, post-tensioned concrete construction has grown and is now one of the most common and economical systems used for multi-story buildings and parking structures. Over the years, post-tensioning (PT) systems have evolved and the industry has learned about various serviceability issues that are magnified in coastal and other aggressive environments. The evolution of the PT systems and potential differences in the long-term performance of each system will be reviewed. In addition, various techniques used to evaluate deteriorated PT and possible repair and monitoring methods used to address deteriorated single-strand systems will be discussed. Several case studies of system and installation specific concerns that can contribute to premature deterioration of PT single-strand systems will be reviewed.