Curtain Wall System Research Articles

IAC/InterActiveCorp Headquarters, New York

This ten-story office building in Manhattan's Chelsea District serves as the corporate headquarters of IAC/InteractiveCorps, one of the world's largest multimedia firms. The 17650 sq.m facility is a sculpted reinforced concrete structure delicately clad with an all-glass, field-fit curtain wall system. The unique design is reminiscent of billowing boat sails on the adjacent Hudson River; and the twisted exterior form produces dramatic angles and spectacular views for the interior office spaces.

A more sustainable curtain wall system: Analytical modeling of the solar dynamic buffer zone (SDBZ) curtain wall

Given the increases in both the environmental and economic costs of energy, there is a need to design and build more sustainable and low-energy building systems now. Curtain wall assemblies are engineered wall assemblies that are used widely in both high-rise as well as low-rise construction. These assemblies show great promise—with the minimal modification outlined in this paper they can be built better now. Often ignored, spandrel panels that comprise a part of curtain wall assemblies can be natural solar collectors. By using a new, simple, low-cost method such as a solar dynamic buffer zone (SDBZ), solar energy can be efficiently gathered or excluded using the movement of air. Such a method can be used in both retrofit as well as new construction. This paper will introduce and outline a proposed SDBZ curtain wall system and present the results of analytical modelling. Using these results, a SDBZ system will be shown to be a more sustainable option for traditional curtain wall assemblies.

Snap, Crackle, Pop: Remediation of a Noisy Curtain Wall

Abstract This case study presents an investigation of disturbing noises emanating from the curtain wall system of a multi-story office building located in the southeastern United States. Shortly after the initial construction of the building, building occupants complained of loud popping noises emanating from the exterior building facade. These noises were of a frequency and magnitude to negatively influence the work environment in adjacent office space. The cause of the noises was investigated by several groups with conflicting results. At the request of the building’s general contractor, an investigation was undertaken to determine the cause of the disturbing noises and to develop remedial recommendations. This investigation included a detailed review of the curtain wall shop drawings and on-site observations to identify questionable details possibly responsible for the noises. The most probable cause of the noises was identified as diurnal solar gain that produced unaccommodated movements in the curtain wall system. The orientation and curvature of the wall combined to allow a thermal expansion that progressed along the wall. The details of the curtain wall construction restrained the movement, leading to sudden release of confining stress. To confirm this hypothesis, affected areas of the curtain wall were instrumented with accelerometers and deflection gages strategically located to pinpoint the origin of the noises. To further confirm the point-of-origin identified by the accelerometers, a series of exploratory openings were made to review curtain wall details. After the source of the noise was positively identified, remedial recommendations to mitigate the disturbance were implemented by the building owner.

Properties and Dynamic Behavior of Glass Curtain Walls with Split Screw Spline Mullions

Recent terrorist events have underscored the importance of designing glass curtain walls as engineered systems. For most building owners, however, it is usually an unjustifiable expense to have a curtain wall designed to provide a high level of blast resistance. This paper investigates the serviceability of an economical, nearly conventional, glass curtain wall system that provides a low level of blast resistance in appropriate applications. A conventional, split screw spline mullion system is utilized with laminated glass lites properly attached to the mullions with structural silicone sealant. The response of this system to service load conditions is first explored through static and dynamic experimental testing. A simple finite-element model of the system is then calibrated to low-amplitude static test results. Finally, the calibrated model is used to perform modal and transient analyses that are compared to experimental free vibration responses. The model was found to provide results that agree well with experimental responses, indicating that the primary properties have been adequately defined for reliable serviceability investigations.

Application of neural networks for the structural health monitoring in curtain-wall systems

In a curtain-wall system, the main and the most possible cause of failures, is the total or partial destruction of its connections with the bearing structure. The present paper deals with the respective health monitoring problem and proposes an Artificial Neural Network (ANN) in order to identify possible imperfections in a typical curtain-wall system. Several Finite Element (FE) models of the curtain-wall system were developed and a parametric analysis was carried out dealing with the loss of rigidity in the aforementioned connections. During the numerical investigations, datasets containing the deflections of the columns of the curtain-wall structure were computed. The obtained results were used to create the Patterns Database, which, in turn, was used as the input for the training of the ANNs. Due to the relatively small number of training patterns, the regularization technique was also employed in order to improve the network generalization. The number of sensors and their optimal placement for appropriate network training were investigated. A wide variety of network architectures was studied and their influence on the network training was analyzed. The obtained results showed that ANNs can be an efficient method for the identification and localization of imperfections in curtain-wall systems.

Full-scale Flexural Strength Testing for Stone Cladding Design

Abstract Beginning with the Industrial Revolution and rapidly increasing following World War II, building cladding systems changed dramatically. Exterior wall construction that had previously consisted of thick mass masonry evolved into contemporary curtain wall systems. As curtain wall systems evolved, the economics of reducing the thickness of curtain wall components became more important. The use of thin stone veneers on buildings in the modern era was not associated with increased knowledge of stone material properties based on testing and research. Rather, the reduction in thickness is attributable to advancements in fabrication technology, economy in construction, and a rational approach to design of veneer systems. This paper will discuss the evolution of the use of stone in curtain wall systems and the associated ASTM standards for building stone. Early ASTM standards for building stone were limited to tests used to evaluate the compression strength of stone which was consistent for mass bearing walls of the early 20th century. As stone was increasingly used more as a veneer, standards for modulus of rupture (ASTM C 99) were introduced. As systems continued to evolve, flexural strength (ASTM C 880) was introduced to address material variability. The evolution of ASTM C 880 included increasing specimen width to further incorporate variability of the stone. Recently, the authors have introduced full panel testing in the design and evaluation process. This paper will present data and discuss the differences in test results for three case studies where both ASTM C 880 specimens and full panel flexural strength testing was performed. The focus of this section will be to discuss the implications of performing full-size panel testing in addition to ASTM C 880 standard specimen testing on design of stone cladding systems for tall building construction as a natural evolution of the design and evaluation process for thin stone cladding systems.

Stiffness Considerations in Dimension Stone Anchorage Design

Abstract Modern building facade design concepts consider all cladding materials, including dimension stone cladding, as nonstructural elements designed to transmit localized gravity and lateral loads to the primary building structural elements. In practice, the structural backup behind dimension stone cladding can take a wide variety of forms, including cast-in-place concrete shear walls, brick and concrete masonry units, aluminum curtain wall system framing, hot and cold rolled steel subframes, and precast concrete panels and members. The flexural stiffness of these backup systems can vary widely, with cast-in-place concrete shear walls on one end of the stiffness spectrum and aluminum curtain framing on the other. The stiffness of dimension stone cladding relative to the backup system can have a significant effect both on the stresses induced in the cladding and the loads transmitted through the cladding anchors. Likewise, the stiffness of the anchor elements and the backup system can affect the loading and stress distribution within the cladding panels. This paper addresses some of the issues associated with the interaction of dimension stone cladding panels, panel anchors, and metal backup structures, and the effects of relative stiffness on load and stress distributions. Information is presented that was obtained from laboratory tests and analyses for new designs, as well as investigations of dimension stone cladding failures.

Insulation plan of aluminum curtain wall-fastening unit for high-rise residential complex

Aluminum curtain wall system is commonly used in high-rise residential complex. For the energy-efficient curtain wall system, the insulation performance of the fastening unit, which enjoins the curtain wall unit to the slab, should be improved because in Korea, hot water pipes for radiant heating are typically installed on the slab in residential buildings. However, this fastening unit composed of metals with high thermal conductivity, acts as a thermal bridge that increases heat loss. Therefore, in this study, we aim to develop a more effective insulation method for the fastening unit. Three alternative fasteners coated with urethane foam and insulation paint were selected (Case 1: using the existing fastener; Case 2: coating the upper part of fastener with urethane foam; Case 3: coating the entire surface of fastener with insulation paint; Case 4: coating the upper part of fastener with urethane foam and the lower part with insulation paint). The heat loss and economical efficiency of each case were analyzed through the three-dimensional annual transient heat transfer simulation and payback period method, respectively. Case 4, compared to Case 1, was found to show the best performance of reducing the annual heat loss by 8.14%. From an economical efficiency perspective, however, Case 2 was found to have the shortest payback period of 2.27years.

Inelastic Dynamic Response of Curtainwall Systems to Blast Loading

Abstract Blast-resistant curtainwall systems require laminated glass that is adequately adhered to the mullions to develop the membrane capacity of the glass, as well as mullions that are capable of transferring the collected forces to the structural slabs. Dynamic inelastic analyses are required to determine the response of curtainwalls to highly impulsive blast loading. The most economical way to minimize the hazard to occupants is to allow the glass to undergo large deformations prior to dismemberment and fragmentation. Curtainwall performance is often evaluated using a sequence of single-degree-of-freedom (SDOF) analyses. The glass is represented as an SDOF to determine the reaction forces, which are then applied to SDOF analyses of the mullions. These individual calculations represent the dynamic inelastic response of the glass and mullions, but often neglect their interaction and phasing. As a result, SDOF methods tend to overpredict the response of the curtainwall components, resulting in an uneconomical design. Dynamic inelastic finite element analyses that account for the interaction of the glass and mullions and accurately represent the potential failure mechanisms provide the most accurate evaluation, leading to the most economical design for blast-resistant curtainwall systems. In addition to material nonlinearities, the finite element analyses also account for geometric stiffening of the components, therefore producing more accurate anchorage forces to be developed at the slabs.

Static finite element analysis of architectural glass curtain walls under in-plane loads and corresponding full-scale test

A pilot study has been conducted to guide the development of a finite element modeling formulation for the analysis of architectural glass curtain walls under in-plane lateral load simulating earthquake effects. This pilot study is one aspect of ongoing efforts to develop a general prediction model for glass cracking and glass fallout for architectural glass storefront and curtain wall systems during seismic loading. For this study, the ANSYS finite element analysis program was used to develop a model and obtain the stress distribution within an architectural glass panel after presumed seismic movements cause glass-to-frame contact. The analysis was limited to static loading of a dry-glazed glass curtain wall panel. A mock-up of the glass curtain wall considered in the analysis with strain gages mounted at select locations on the glass and the aluminum framing was subjected to static loading. A comparison is made between the finite element analysis predicted strain and the experimentally measured strain at each strain gage location.

Understanding terra-cotta distress: Evaluation and repair approaches

This paper will provide a brief history of terra-cotta veneer systems in general and specifically representative examples of terra-cotta-clad building systems in the United States. Through case studies, various types of distress, the causes of distress, and repair techniques of the distress will be discussed. Distress in terra-cotta facades often manifests as cracking or displacement of terra-cotta units. More than other modern curtain wall systems, terra-cotta is a hybrid system and distress may result from a number of causes. Common repairs including replacement, removal, and reinstallation, and in situ through face pinning may all be appropriate depending on the cause of distress. The underlying cause of distress must be understood, so that a durable repair and appropriate maintenance programme can be established.

Seismic Performance of Two-Side Structural Silicone Glazing Systems

Abstract This paper presents the results of the first phase of an experimental research program on simulated seismic performance of structural silicone glazed (SSG) curtain wall systems. Full-scale, two-side SSG mockups made up of three side-by-side glass panels were tested under cyclic racking displacements to determine serviceability and ultimate behavior responses. Variables were glass type (annealed and fully tempered) and panel configuration (monolithic, laminated, and insulating glass). In the experiments carried out, damage states such as gasket deformation/pullout, sealant failure (e.g., adhesion/cohesion, etc.), glass cracking glass and fallout were identified and their corresponding drift levels were determined. The extent of damage to silicone sealant was determined through air leakage tests.

Curtain Wall Designs for Wind and Blast: Three Case Studies

Current design for curtain walls subjected to wind, wind-borne debris, and blast contain relatively new structural requirements for the curtain wall designer to address. These new criteria are defined and discussed in application to three case studies of curtain wall systems. The case studies illustrate the impact of these criteria on modern curtain wall designs and offer conclusions regarding the process and impact of designing curtain walls to current standards. It is concluded that projects in hurricane regions require fairly stout deigns and can withstand moderate blast loads. Wind tunnel testing remains a viable option to define design load criteria. Even low-rise building projects in high-velocity wind zones can benefit from wind tunnel modeling due to more precise and often reduced design pressures.

Designing Concrete Precast External Wall Components on Multi Storey Steel Stuctures According to Modular Co-ordination

Lightweight curtain wall systems and precast concrete wall panels are commonly used in steel skeleton external wall construction. The design of external wall components must incorporate modular-dimensional coordination rules. Modular design of external walls reduces component types and increases the buildability of façades. The purpose of this study is to research the adaptability of large standard precast wall panels to steel skeleton structures according to the modular coordination rules. In addition, according to the possible locations of the wall panels in the façades, design dimensions are calculated and types of panels are recommended in conclusion.

Glass in Compression Leads to Panels without Holes

The structural design of three structures using toughened glass sheets in compression to act as load-bearing shear walls is described. In each case a strong, transparent facade is achieved without the need to make holes in the glass sheets. For small projects it is often not economic to make holes in the glass to allow suspension from above in a curtain-wall system. It is better to use the glass in compression as a simple stack to carry the self-weight directly down to the foundation. The stack can then also be used as a shear wall to carry sway loads acting on the building. In order of completion date and scale three projects in Japan are described: a shop enclosure screen, a dental surgery, and a seminar hall facade.

Effect on Thermal Comfort of Radiant Heat Exchange Near Single Glazed Windows

It has become common practice over the last two decades to clad commercial buildings with curtain wall systems with large windows. Typically viewing panes are continuous around the building perimeter and extend from sills at about 900 mm above the floor to the ceiling line. Anecdotal evidence has suggested that people in the vicinity of these windows can suffer from hot and cold discomfort depending on season and time of day. This paper will report the results of a longitudinal investigation of these phenomena spanning two years in a typical office building in an inner suburban business district. It was found that radiant asymmetry and associated diurnal temperature shifts had a significant impact on thermal comfort in proximity to the windows. A difference of one comfort vote interval could be attributed to a frontal radiant temperature difference of about 2.8 oC. A 33 oC difference brought about a one vote difference for persons side on to the radiant source/sink. Also change in operative temperature in perimeter zones as the sun moved around the building had the effect of moving the comfort vote approximately one interval for every two degrees of shift over approximately three hours.

Dynamic Racking Performance of an Earthquake-Isolated Curtain Wall System

Dynamic racking tests, coupled with air leakage tests, were performed on fullsize specimens of a new, Earthquake-Isolated Curtain Wall System and a widely used, conventional curtain wall system (used as an experimental control). Dynamic racking tests simulated seismic movements that could be imposed upon a curtain wall system as a result of interstory drifts. Air leakage tests were performed as an indicator of serviceability performance of both curtain wall systems during the dynamic racking tests. The Earthquake-Isolated Curtain Wall System demonstrated strongly superior performance in terms of both serviceability (glass cracking and air leakage) and life safety (glass fallout). The conventional system exhibited vulnerability to annealed monolithic glass cracking and glass fallout at dynamic racking drift indices of 1.9% and 3.1%, respectively. No glass damage was observed in the earthquake-isolated system up to the dynamic racking displacement limit of the test facility, which corresponded to a drift index of 4.9%. Air leakage rates through vision panels in the conventional system remained constant up to a drift index of 1.9%, after which the air leakage rates increased rapidly. In contrast, air leakage rates through vision panels in the earthquake-isolated system remained unchanged up to the 4.9% drift index capacity of the test facility.

Study on pressure-equalization of curtain wall systems

Abstract In recent years, aluminium-curtain-wall systems are often used in southeast Asia. Many of these curtain-wall systems can be classified as a two-barrier system with a front-panel (the rainscreen) and the back-panel (the air barrier). The back-panels of such systems are usually thin and flexible. Compared with the brick or brick-veneer rainscreen walls, where the back-panels are very rigid, the pressure-equalization characteristics are expected to be quite different. To improve on the understanding of the behaviour of such systems and to evaluate design parameters, full-scale measurements were carried out. A numerical model which takes into account the flexibility of the back-panel has been developed for the prediction of cavity pressure in curtain walls. The results based on this model show good agreement with those obtained from full-scale experiments.

Nonlinear finite element analysis of glass panels

Glass panels which are widely used in curtain wall systems, behave nonlinearly under high wind load when their deflections exceed about 3/4 of their thickness. The American and the Canadian design codes for curtain wall and window systems have made it mandatory to include the effect of large deflection in the design and analysis of glass panels. This paper presents a versatile finite shell element method for nonlinear analysis of glass panels subjected to high wind loads. The accuracy of the proposed method is demonstrated via comparison with the results of previous studies and experiments. The advantage of the present method is its versatility in handling complex loading and boundary conditions whilst its longer computational time has been effectively offset by the adoption of the efficient incremental-iterative minimum residual displacement method of analysis and the availability of fast personal computers. Using the examples studied in this paper, it was found that the nonlinearity in glass may violate the linear assumption in the practical loading range, resulting in unexpected glass behaviour if the linear theory is used. More interestingly, the use of higher strength glass, the tempered or the heat-strengthened glass, will not increase the load resistance of the panel when it is under in-plane loads causing instability.

Dynamic racking tests of curtain wall glass elements with in‐plane and out‐of‐plane motions

AbstractThis project was conducted to investigate the breakage and fallout behaviour of various types of architectural glass elements in a dry‐glazed curtain wall system under in‐plane and out‐of‐plane dynamic motions. The project was a follow‐up to an earlier project that focused exclusively on in‐plane dynamic racking performance of curtain wall glass elements. The recent data indicated that adding out‐of‐plane motions caused significantly higher amounts of glass breakage and subsequent glass fallout in most glass types that were found during the in‐plane tests to be prone to glass fallout. Specifically, 1/4 in (6 mm) annealed monolithic glass, 1/4 in annealed monolithic glass with a 0·004 in (0·10 mm) PET film (not anchored to the mullions), and 7/16 in (11 mm) fully tempered laminated glass exhibited comparable or higher fallout rates than the already substantial fallout rates that were observed during the in‐plane only racking tests. Unanchored window film was found to be ineffective in resisting post‐breakage glass fallout under dynamic racking motions. In contrast, 1/4 in (6 mm) annealed laminated glass and 7/16 in (11 mm) heat‐strengthened laminated glass exhibited no glass fallout during the out‐of‐plane tests, just as they exhibited no fallout during the in‐plane tests. Out‐of‐plane test results also showed that 3/8 in (10 mm) heat‐strengthened monolithic glass exhibited no fallout, while 3/8 in annealed monolithic glass exhibited very negligible glass fallout. The addition of torsional motions was not found to induce glass fallout in those glass types that resisted glass fallout in previous tests performed without torsional motions.