Glass Curtain Wall Research Articles

Experimental and numerical investigation of cyclic response of a glass curtain wall for seismic performance assessment

In contemporary architecture, the use of the glass curtain walls is increasingly growing. However, after experiencing earthquake motions, they have sometime shown damage, which might cause considerable life-safety hazards for pedestrian and occupants of buildings, as well as significant economic losses to owners, due to downtime and cost for repairing. This work aims to investigate the behaviour of such systems under seismic loads, so to contribute to the enhancement of the capability of designers and manufacturers in dealing with seismic vulnerability of glazed systems and reducing earthquake induced losses. This study shows cyclic experimental tests performed at the Construction Technologies Institute (ITC) of the Italian National Research Council (CNR) for seismic performance assessment of a full-scale aluminium-glass façade, designed and manufactured according to a standard technology for the European market. A non-linear finite element model has been calibrated according to experimental results. The aim is understanding further aspects of the lateral behaviour of these non-structural elements and also giving useful information for numerical simulations of similar façades, that in the next future should be performed even in the absence of experimental data.

Debonding Detection in Hidden Frame Supported Glass Curtain Walls Using the Nonlinear Ultrasonic Modulation Method with Piezoceramic Transducers.

Debonding defects are common and they are the main reason for the failure of hidden frame supported glass curtain walls, which are widely used as an external enclosure and decorative structure. In this paper, a debonding detection method for hidden frame supported glass curtain walls is developed based on nonlinear ultrasonic modulation and piezoceramic transducers. First, the excitation frequency was determined according to the response characteristics. Then, empirical mode decomposition (EMD) was applied to extract the feature components. After discrete Fourier transform (DFT), the nonlinear coefficients were calculated to evaluate the debonding defect. Finally, the experimental setup was established and a series of experiments were carried out to verify the feasibility and effectiveness of the nonlinear ultrasonic modulation method. The nonlinear harmonics detection method was also investigated and it was compared with the nonlinear ultrasonic modulation method. The detection effect at different temperatures and impact were studied. The results showed that the nonlinear coefficient increases with the debonding length. The mean squared error (MSE) of the nonlinear ultrasonic modulation method was improved by 41% compared with the nonlinear harmonics method. The nonlinear ultrasonic modulation method can successfully detect debonding defects in hidden frame supported glass curtain walls at different temperatures and impact.

Toward ultra-low reflectance semi-transparent organic photovoltaic cells with biomimetic nanostructured transparent electrode

Abstract Semi-transparent organic photovoltaic cells (STOPVs) hold the great potential as a solar conversion source installed on the glass curtain walls. The cell performance of STOPVs is to some extent balanced among the absorption, transmission and reflection of the incident solar radiation. For the practical application with a defined transparency, the efficiency of STOPVs can be optimized by maximizing the light absorption as well as minimizing the reflection that contribute to the light pollution. Herein, a low-reflectance STOPV is presented with relatively high efficiency, high transmittance, and suitable color rendering property. A 15.9% increase in photocurrent and a 28% decrease in reflection are realized with the implementation of biomimetic moth-eye nanostructures into the dielectric-metal-dielectric transparent electrodes. For an optimized PTB7:PC71BM-based STOPV on flexible plastic substrate, the average transmittance in the visible region is kept at 46.1% and the average reflectance is reduced to 10.3%, leading a power conversion efficiency of 3.4%. The pathway described here is promising for opening up opportunities of reliable STOPVs towards the future commercial applications.

Interfacial Adhesion–Strength Detection of Structural Silicone Sealant for Hidden Frame–Supported Glass Curtain Wall Based on Nonlinear Ultrasonic Lamb Wave

AbstractDegradation of interfacial adhesive strength is the main reason for failure of the hidden frame–supported glass curtain wall that is now widely used in the construction field. In this paper...

Rapid evaluation of safety-state in hidden-frame supported glass curtain walls using remote vibration measurement

The vibration performance of a simulation for a hidden-frame supported glass curtain wall (HFSGCW) was tested using a Laser Doppler Vibrometer (LDV) in this paper. The effect of silicon structural sealant on the first order inherent frequency of HFSGCW and the spectral characteristics per LDV on different points were studied. Meanwhile, the test results of LDV were verified using traditional sensors (DASP modal analysis system) in order to evaluate the feasibility of LDV used for safety state evaluation of HFSGCW. Results show that the first order inherent frequency obtained by LDV matches well with DASP modal analysis results. The first order inherent frequency decreases with an increase of sealant failure，and the first order frequency amplitude scale of structural sealant upper point increases significantly after the structural silicon sealant is destroyed. The safety state of HFSGCW is divided into three levels. Meanwhile, a safety state rapid evaluation model and key detection technologies of HFSGCW based on LDV is proposed.

Study of Tensile Bond Strength for Structural Silicone Sealants after Artificial Accelerated Aging

Tensile bond strength is one of the most significant properties for structural silicone sealants used in the glass curtain walls. During the service process, aging of the silicone sealants shall be involved in comprehensive actions of environment factors, e.g. temperature, humidity, and ultraviolet light etc. In this study, artificial accelerated aging test was conducted to make clear the development of tensile bond strength, Shore hardness and elongation. The test results show that: (i) the specimens under damp-heat test have more degeneration than specimens under humidity-freeze test; (ii) the environment of high temperature and high humidity leads to the change of tensile bond, Shore hardness, elongation, and results in interfacial failure of samples.

Study on construction technology of metro tunnel under a glass curtain wall

To ensure the safety of the glass curtain wall building above loess tunnel and get an optimal scheme, an elastic-plastic FEM model is established to simulate three reinforcement schemes based on a tunnel section in Xi’an Metro Line 3. The results show that the settlement value of the optimal scheme is reduced by 69.89% compared with the drainage measures, and the uneven settlement value is reduced by 57.5%. The construction points, technical processes and technical indexes of the optimal scheme are introduced. According to the actual project, the cumulative settlement of the building under construction is 16mm, which meets the control standards. According to the actual project, the cumulative settlement of the glass curtain wall building is 16mm, which meets the control standards. The reinforcement scheme can provide some reference for the design and construction of the metro in loess area.

The influence of fire size on breakage time for double glazed curtain wall system in enclosure fire

The prediction of breakage time on curtain wall system is an important factor for the fire protection system in high-rise buildings. The breakage of glass is caused by thermal deformation of curtain wall frame. Also, thermal deformation could be influence by fire size. Therefore, in this study, numerical analysis is performed to investigate the effect of fire size on breakage time on double glazed curtain wall system. To investigate the effect of fire size on breakage time, the pool size is varied 0.4x0.4 m, 0.5x0.5 m and 0.6x0.6 m, respectively. As a result, the breakage times of glass are decreased as 170 s, 100 s and 38 s for the pool size varying 0.4x0.4 m, 0.5x0.5 m and 0.6x0.6 m, respectively. From the numerical results, the present study suggests the useful relationship between the heat release rate and breakage times as follow: t = -0.341×Q e + 257.64 (252.3 kw < Q e < 637.9 kw). In order to prevent breakage of glass curtain wall due to fire, fire protection system must be operated

Theoretical and experimental research on influence of cavity frequency difference in birefringent laser feedback system

The internal stress of glass material directly affects the processing quality of glass components and the service life of optical components. It is an important factor that relates to the overall system performance, safety, and reliability. Aerospace, precision optical systems, precision machining and other areas generally highly value the stress measurements of glass components. For example, the internal stress in the medium-glass material of precision imaging system will lead to the degradation of optical performance and reduce the image quality; the stress in the glass material used as the gain medium of high-power solid-state lasers not only directly affects the polarization state of the output light, but also shortens the service life of the laser; the stress concentration in the load-bearing glass of aircraft windshields, building glass curtain walls, etc., will cause serious accidents such as popping due to the reduction of glass mechanical properties. Therefore, the high sensitivity and large measurement range of stress detection technology has become a current research hotspot. Stress measurement techniques based on the birefringent external cavity laser feedback effect has received widespread attention due to its advanced and novel measurement principle. It is generally accepted in the traditional theory that the output phase of the laser in a feedback system is only determined by the phase retardation of birefringent element in an external cavity, and the measurement error is induced by the non-linear movement of external mirror. In this paper, the orthogonally polarized laser principle and the three-cavity equivalent model are combined to explain the influence of cavity frequency difference on the output of laser in feedback system. The frequency difference caused by the birefringence of the laser cavity is measured by comparing the intervals between adjacent longitudinal modes, and the frequency tuning feedback experiment is carried out. Theoretical analysis and experimental results show that the output phase of the laser is determined by the phase retardation of the external cavity, the frequency difference of the internal cavity, and the length of the external cavity. This conclusion is also confirmed by the measurement of the standard quarter wave plate. For a feedback system with an internal cavity frequency difference of 5 MHz and external cavity length of 150 mm, the phase difference induced by internal cavity frequency difference is about 0.573. The laser can output a single longitudinal mode below 40 MHz of the internal cavity frequency difference, and the length of the external cavity is generally larger than 150 mm when the actual system is designed, so the phase difference introduced by these two parameters cannot be ignored and must be calibrated. This study summarizes the phase characteristics of the orthogonally polarized laser under the joint of anisotropy feedback cavity, supplements the physical content of the laser feedback, and has great significance for accurate laser measurement of stress-birefringence, displacement, and distance.

Numerical assessment of vibration control systems for multi-hazard design and mitigation of glass curtain walls

Glass systems and facades are widely used in building structures, due to a multitude of aspects. Beside these motivations, from a pure structural point of view, glazing envelopes represent one of the most critical components for multi-storey buildings under the action of exceptional loads as impacts, explosions, seismic events or hazards in general. Such systems represent in fact the first line of defense from outside. Given the current lack of specific design regulations for the mitigation and enhancement of glass curtains under extreme loads, as well as the typically brittle behaviour and limited tensile resistance of glass as material for constructions, the same facades require specific, fail-safe design concepts.In this paper, the feasibility and potential of special mechanical connectors interposed at the interface between a multi-storey primary building structure and the enclosing glazing facade are investigated via accurate Finite-Element (FE) numerical models, under various impact scenarios. At the current stage of research, careful consideration is given both to the observed global performances as well as to local mechanisms, based on computationally efficient FE models inclusive of damage models to account for failure mechanisms in each system component. Compared to earlier research efforts, the attention is focused on the multi-hazard performance of a given case study building, subjected to extreme loadings such as seismic loads or blast events. As shown, even the typically different features of the examined loading conditions, when the proposed vibration control devices are properly designed and the curtain wall is considered as part of a full 3D building, the final result is an overall assembled structural system in which the glazing facade can work as a passive control system for the building system, in the form of a distributed Tuned-Mass Damper (TMD), with marked benefits in terms of protection level as well as design optimization.

Downdraft Assessment of Glass Curtain Wall Buildings with a Radiant Floor Heating System

The present study aims to evaluate whether downdraft can be prevented by applying a radiant floor heating system in glass curtain wall buildings. A radiant floor heating system does not directly supply heat to cold air, but does so via heat exchange with a cold airflow. Assessing whether a downdraft is prevented is, thus, necessary. For this assessment, a radiant floor heating system was applied to perimeter zones with different window types modeled using a computational fluid dynamics (CFD) simulation. The relationship between the radiant floor heating system and the windows was examined via an assessment of the resulting downdraft by considering the radiant heat exchange effect between the window and the floor. The assessment was conducted by utilizing a CFD simulation. The simulation results show that the temperature difference between the air supplied through the radiant floor heating system and the air descending along the cold surface of the window increased when the radiant floor heating system was applied to a narrow area with a high temperature. Furthermore, the airflow velocity increased with the heat exchange. The airflow re-entered the window side, and the downdraft in the occupied area exceeded the strict value specified by the standards. Conversely, if heat were applied according to the indoor thermal output by widening the radiant heat area of the radiant floor heating system, a downdraft could occur as a result of a blocking failure prior to the influx of the cold air into the occupied area caused by low surface temperatures. Therefore, applying a radiant floor heating system is advantageous in a perimeter zone without causing airflow inducement at the window side with acceptable surface temperatures.

Validation of a numerical model for curtain walls with MVHS during free burning

Glass breakage of curtain wall coverings during a fire can promote the spread of a fire in high-rise buildings. Prior to the development of sprinklers to prevent and delay glass breakage, it is necessary to identify the breakage mechanism of curtain wall glass panes and to establish a numerical model to simulate various fire situations using sprinklers to design effective sprinkler systems. The present study was conducted to establish a numerical model and analysis procedures to simulate fire situations. First, curtain wall was installed on one side of a testing chamber that was 3 m (L) × 3.2 m (W) × 2.4 m (H), and a free burning experiment was conducted using heptane. The same experimental conditions were simulated using a numerical model employing the modified volume heat source (MVHS) model. To analyze the validity of the numerical model, the air temperature inside the room and the surface temperatures of the curtain wall Al frame and glass panes calculated by numerical analysis were compared with experimental values, and the location and timing of the initial crack were compared. Thermocouples were installed on the Al frame and the glass surface to measure the surface temperature of the curtain wall during the fire for approximately 100 s after the onset of the fire. Additional thermocouples were installed to measure the air temperature inside the room to verify the results of the numerical analysis. A numerical model using the MVHS model was established to analyze the overall temperature distribution and the behavior of thermal stress on the curtain wall caused by the fire. MVHS calculations were based on measured fuel consumption, and the numerical analysis results were compared with the experimental values. We confirmed that the temperature calculated using computational fluid dynamics (CFD) was in good agreement with the temperature measured in the experiment. The temperature distribution and thermal stress of the curtain wall up to the point of glass breakage were reviewed using a thermal stress structural analysis that employed the results of the CFD analysis with MVHS. The time required to reach the temperature required for glass to break in the numerical analysis and the time required for the first crack to occur in the experiment were identical. The crack positions obtained from the numerical model and experiments were also the same. Overall, our results showed that the numerical model using the MVHS model is suitable for predicting curtain wall breakage and temperature distributions inside a space during the fire.

False Windows - Yesterday and Today

The article is concerned with a very interesting aspect of architectural design, namely, a contradiction between the building functions and the necessity of giving the building a desired external appearance. One of the possibilities of reconciling this contradiction is using pseudo windows that are visible on the elevation and generally have the form of a black painted recess accompanied by frames and sashes and often single glazing. Of course, there are no windows or openings in the corresponding places in the walls inside the building. The article discusses the differences between false windows and blind widows (German: blende), also known as blank windows, which, in fact, are shallow recesses in the wall having the external appearance of an arcade or a window and which had already been used in Gothic architecture mostly for aesthetic reasons and sometimes to reduce the load of the wall. Moreover, the article describes various false windows that appeared later than blind windows because they did not appear until the 17th century. Contemporary false windows are also discussed and it is shown that contrary to the common belief they are widely used. In his research, the author not only used the Internet data but also carried out his own in situ exploration. The false windows constitute very interesting albeit rare elements of the architectural design of buildings. They have been used successfully for a few hundred years. It might seem that they should have been discarded by now but this has not happened. Quite contrary, since the second half of the 20th century there has been a rapid development of glass curtain walls that serve a similar function in contemporary buildings as the false windows once did, only in a more extensive way.

Passive Control Systems for the Blast Enhancement of Glazing Curtain Walls Under Explosive Loads

Glass curtain walls are used in modern buildings as envelopes for wide surfaces due to a multitude of aspects. In glass curtain walls, tensile brittle panels are connected - through mechanical or adhesive joints - with steel frameworks or aluminum bracing systems, and due to the interaction of several structural components, the behaviour of the so assembled system is complex to predict, especially under exceptional loading conditions such as explosive events. In the paper, glazing curtain walls are investigated by means of Finite-Element (FE) numerical simulations, under the effect of air blast pressures of variable intensity. Their typical dynamic behaviour and criticalities under high-strain impact loads are first analyzed. By means of extended nonlinear dynamic FE parametric studies, innovative devices are applied to traditional curtain walls, at their support points, in order to improve their expected dynamic response. Two possible solutions, namely consisting of viscoelastic (VE) or elasto-plastic (PL) dampers, are proposed as passive control systems for the mitigation of maximum effects in the façade components deriving from the incoming blast pressures. As shown, although characterized by specific intrinsic mechanical behaviours, either VE or PL dampers can offer beneficial structural effects. In the first case, major advantages for the façade components derive from the additional flexibility and damping capacities of VE devices. In the latter case, PL dampers introduce additional plastic energy dissipation in the traditional curtain wall assembly, hence allowing preventing severe damage in the glazing components. It is thus expected that the current outcomes could represent a valid background for further experimental validation as well as detailed assessment and optimization of the proposed design concept.

Experimental study on fire response of double glazed panels in curtain walls

Double glazing is increasingly employed in glass curtain walls, but very little is known about its thermal response under fire conditions. In this work, a total of twenty seven 600 × 600 mm2 double glazing units, with 6 mm, 9 mm and 12 mm air spacings, were tested. Three different installation types were adopted: 1) exposed frames, 2) horizontal-hidden frames and 3) vertical-hidden glass in order to study their potential effects on the glazing breakage behavior. A 500 × 500 mm2n-heptane pool fire was used to heat the glass panes. The breaking time, surface temperature, total heat flux, heat release rate, and crack and fallout morphology were measured and analyzed. The test result suggests that different installation types have a significant effect on the fracture behavior of double glazing, especially for glass panes located at the fire side. Glass in exposed framing is more prone to cracks than those in semi-exposed frame, but fallout may more easily occur in semi framing façades. When no, or very limited fallout occurs at the fire side pane, thicker air space leads to a longer breakage time of ambient glass panes, thus improving the unit's integrity during fire. The experimental results obtained in this study is valuable for the development of practical guidelines for fire safety design.

Topology optimization of the photovoltaic panel connector in high-rise buildings

Photovoltaic (PV) panels are used in high-rise buildings to convert solar energy to electricity. Due to the considerable energy consumption of high-rise buildings, applying PV technology is of great significance to energy saving. In the application of PV panels, one of the most important construction issues is the connection of the PV panel with the main structures. One major difficulty of the connection design is that the PV panel connection consists of two separate components with coupling and indeterminate dimension. In this paper, the gap element is employed in these two separated but coupled components, i.e., hook and catch. Topology optimization is applied to optimize and design the cross-section of the PV panel connection. Pareto optimization is conducted to operate the optimization subject to multiple load scenarios. The initial design for the topology optimization is determined by the common design specified by the Technical Code for Glass Curtain Wall Engineering (JGJ 102-2003). Gravity and wind load scenarios are considered for the optimization and numerical analysis. Post analysis is conducted for the optimal design obtained by the topology optimization due to the manufactory requirements. Generally, compared with the conventional design, the optimized connector reduces material use with improved structural characteristics.

Challenges of modern materials: assessment and repair

ABSTRACTModern materials present unique challenges in terms of assessing performance and evaluating whether these materials can be repaired, restored, and conserved, or whether they need to be replaced – based on criteria including inherent significance and integrity, anticipated performance, durability, resiliency, and potential for continued use. Some specific issues encountered with modern materials include questions related to weathering, lack of redundancy, and the use of innovative but inherently non-durable materials and assemblies. The effects of material weathering (patina) may be considered desirable on handcrafted materials but is often less acceptable on highly machined materials typical of modern buildings. While the weathered appearance of traditional materials may be considered tolerable or even desirable, some modern buildings may demand frequent treatment to achieve a consistently new appearance. The inherent lack of redundancy in modern thin claddings such as thin stone veneer and resin panels, as well as glass and metal curtain wall systems, presents complex problems that were not historically of concern with traditional materials. For example, modern materials and systems are less forgiving of water leakage than traditional masonry wall construction; issues of strength loss and anchorage deterioration are of greater concern with modern thin claddings. Finally, some modern materials and systems have a limited life span and are far more demanding in terms of cyclical maintenance than traditional materials, while changes in production have rendered some materials obsolete and difficult or impossible to duplicate exactly if replacement is required. Innovative materials also present particular challenges if they have not performed well over time or contain hazardous components. However, if the materials are significant and character-defining, they will likely warrant preservation based on technical uniqueness and in order to preserve the original architectural intent. This article examines a range of modern materials and their characteristics in light of these issues and criteria, illustrated with examples from recent projects involving thin stone and resin cladding panels, glazing systems, and coatings and sealants, among others, with comparison to traditional materials where appropriate. The article also seeks to inform the development of conceptual guidelines for the assessment and repair, restoration, and conservation of modern materials.

Design and Realization of the Claw Gripper System of a Climbing Robot

Climbing robots are widely used to inspect smooth walls, such as glass curtain walls and ceramic tile surfaces. However, a good adsorption method for inspecting a cliff face and dusty high-altitude buildings with small-amplitude vibration has not been found. In this study, a new adsorption method using grasping claw grippers to adhere to rough walls is proposed and applied. A mechanical model for the interaction between the gripper and the uplifts on rough walls is also established to analyze the critical state of force balance of the gripper. In addition, MATLAB is used in a simulation, and an experimental prototype is designed to test the grasp stability of the gripper. Simulation and experiment results indicate that the gripper can adequately achieve grasping adsorption on a rough concrete wall. The findings provide a foundation for constructing a system for a rough-wall-climbing robot.

Discussion on Structure Design and Optimization of Building Curtain Wall

To discuss the structure design and optimization of building curtain wall, the dynamic characteristics of point supported glass curtain wall system are analyzed by the finite element method. The various technologies are made use of, and according to the characteristics of the structure system, the finite element analysis model with steel structure glass plate beam element and shell element as the basic elements is established. Then, the dynamic characteristics are analyzed, and the modal parameters such as inherent frequency and vibration type are identified. The research results show that the node displacement response power spectrum under the load of wind is obtained, which provides the basis for rationally optimizing the structure. Based on the above findings, it is concluded that the optimization design based on finite element model has a wide significance, which is a useful attempt to reduce the blindness of design and has great engineering significance and application value.

Wind-Induced Response of an L-Shaped Cable Support Glass Curtain Wall

Due to its flexibility, cable support glass curtain wall is sensitive to wind loads and its wind-induced dynamic response has attracted more and more attention recently. However, the wind-resistant study for this kind of structure mainly focuses on single-layer plane cable support curtain walls but is rare on irregular ones. In this paper, the wind-induced response of an L-shaped cable support glass curtain wall is analyzed. In order to truly reflect the force transmission, a finite element model of curtain wall is established to ensure collaborative deformation between glass and cable, including glass panel, cable, sealant, and claw connection. Time-domain vibration analysis of the curtain wall is carried out with the random sequence of multinode fluctuating wind velocity time history simulated by autoregressive linear filtering method based on Kaimal wind velocity spectrum. Four wind flow directions are specified, namely, 0°, 15°, 30°, and 45°, to analyze the wind-induced dynamic response of this structure with consideration of the fluid-structure interaction effect. Finally, the deflection of the glass surface is studied by statistical analysis of displacement so as to obtain the wind vibration coefficient suitable for structural design of practical projects, and the variation of cable force is investigated as well.