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In cold-formed steel building construction, cold-formed steel shear wall panels (CFSSWPs) are used as primary lateral load resisting components, that maintain the stability and the integrity of the structure. Traditionally, a CFSSWP constits of a cold-formed steel frame with structural sheeting, such as oriented strand board (OSB), gypsum wall board (GWB), plywood or other, screwed onto it. These type of elements have some unique properties, such as high elastic stiffness, large displacement ductility, etc. On the other hand, as the studs are closely spaced - a value of 60 cm for the spacing is common - only small openings are present, hence transparency is limitted; To increase the transparency of cold-formed steel buildings, which is a tendency in contemporary architecture, load-bearing capacities of glass can be utilised by bracing the frames with glass instead of traditional sheeting. The conventional two-component structural silicone Sikasil (R) SG-500 is considered for the load-bearing cold-formed steel-glass connection. In this research, the racking behaviour of 1.5 m by 3.5 m cold-formed steel frames onto which glass panels are circumferentially bonded on both sides is determined by means of experimental tests. This paper reports about the conducted experiments and the obtained data. From the tests, a value of 32.25 +/- 0.452 kN/m was obtained for the racking strength of the considered hybrid cold-formed steel-glass panels. A comparison with traditional CFSSWPs showed that the hybrid element can obtain similar racking strengths. Therefore, the study revealed the potential of hybrid cold-formed steel-glass elements using structural silicones to provide sufficient in-plane lateral stiffeness and strength.

Summary A test environment to evaluate the seismic performance of gusset plate connections intended for steel braced frames is proposed. The developed test method combines the substructuring techniques with finite element analysis methods in an on-line hybrid scheme. Numerical substructure analysis is conducted on bracing members, while bracing connections are treated as experimental substructures. A force-displacement combined control imposed with the aid of 2 jacks ensures physical continuity between the analysis and test. The rotational behavior of gusset plate connections subjected to large inelasticity and varying axial loading until fracture is investigated. Two gusset plate details were designed and tested to verify the efficiency of the proposed method. The test method is rational, and smooth operation is achieved. The test results revealed the advantage of the developed on-line hybrid test method in exploring the ultimate capacity of bracing connections.

Sensitivities of the buckling and post-buckling responses of braced moment resisting frame (BMRF) systems to initial imperfections in their gusset-brace sub-systems are studied. Previously, the effects of imperfection amplitude and type have not been evaluated in requisite detail, and only a general recommendation—which is given as a function of the bracing element's length—has been utilized. Here, highly detailed (centimeter scale) three-dimensional finite element models are employed in parametric sensitivity analyses to quantify the effects of imperfections on the responses of BMRFs with diagonal and X-bracing subsystems. The results are discussed and amendments are proposed to the existing empirical equations for evaluating the buckling and post-buckling capacities of imperfect bracings. The parametric studies showed that while an increase in the imperfection amplitude can dramatically decrease the initial buckling load of BMRFs, this causes only moderate decreases in their post-buckling strengths, and their ultimate states remain nearly unaltered.

The new multifunctional hall of Falkonergardens Gymnasium and the associated foyer opened in 2015 and can be used by up to 1,000 people. The same year, it was awarded a prize by Frederiksberg Municipality as one of the city's finest buildings. In 2016, the building also received this year's “Store Arne”, awarded annually by the Danish Association of Architects for work that raises the standards of architecture in Copenhagen. The ‘multihall’ for Falkonergarden in Copenhagen has a covered steel structure. It is a structure that maximizes the use of the shape with interacting plate action and “membrane” action in the cylindrical walls. The basic structural behavior is without use of primary structural members in bending. It has an orthogonal space structure for the upper roof; it has no horizontal bracing, but is only stabilized for horizontal shear forces by a closed kidney-shaped ring beam without bending. The structural spaceframe roof has maximized the production possibility of the use of large fully fabric-welded trusses bolted together on site with welded plane cross members. The structural design of the roof space frame allowed erection in only two days without use of scaffolding. Very simple structural freeware has been a help in the sketch design stage. The aim of the steel design was to find a synthesis of architecture, structural behavior, productivity and buildability. It was a very challenging job, although full understanding is only for people with X-ray eyes! (Fig. 1 and 2).

Due to the low tensile strength of masonry perpendicular to the bed joint, masonry wall panels have non-linear material properties. Assuming simple elastic constitutive laws, this article presents two modelling variants, which consider the lack of tensile strength in a simple manner. Both variants are investigated for their advantages and disadvantages. In a second part of the article, the application of the methods will be illustrated through the example of a four-storey building.

Summary Beam–column sub-assemblages are the one of the most vulnerable structural elements to the seismic loading and may lead to devastating consequences. In order to improve the performance of the poorly/under-designed building structures to the critical loading scenarios, introduction of steel bracing at the RC beam–column joint is found to be one of the modern and implementable techniques. In the present work, a diagonal metallic single haunch/bracing system is introduced at the beam–column joints to provide an alternate load path and to protect the joint zone from extensive damage because of brittle shear failure. In this paper, an investigation is reported on the evaluation of tae influence of different parameters, such as angle of inclination, location of bracing and axial stiffness of the single steel bracing on improving the performance through altering the force transfer mechanism. Numerical investigations on the performance of the beam–column sub-assemblages have been carried out under cyclic loading using non-linear finite element analysis. Experimentally validated numerical models (both GLD and upgraded specimen) have been further used for evaluating the performance of various upgrade schemes. Cyclic behaviour of reinforcement, concrete modelling based on fracture energy, bond-slip relations between concrete and steel reinforcement have been incorporated. The study also includes the numerical investigation of crack and failure patterns, ultimate load carrying capacity, load displacement hysteresis, energy dissipation and ductility. The findings of the present study would be helpful to the engineers to develop suitable, feasible and efficient upgrade schemes for poorly designed structures under seismic loading. Copyright © 2016 John Wiley & Sons, Ltd.

Sandwichelemente werden als Dach- und Wandbauteile derzeit ausschlieslich auf eine tragende Unterkonstruktion montiert. Sie sind deshalb als Sekundarbauteile eines Gebaudes zu betrachten und werden als selbsttragende Bauteile klassifiziert. In statischer Hinsicht sind sie jedoch Ein- oder Mehrfeldtrager, die neben ihrem Eigengewicht auch Wind- und Schneelasten abtragen. Es sind lediglich Biegemomente und Querkrafte vorhanden. Bei Gebauden aus Sandwichelementen ohne Unterkonstruktion werden die Paneele zusatzlich in ihrer Ebene belastet. Dies geschieht zum einen in vertikaler Richtung als lastabtragende Wandscheibe, zum anderen als aussteifende Dach- oder Wandscheibe. Dieses Tragverhalten wurde am Institut fur Sandwichtechnik (iS-mainz) der Hochschule Mainz in Axial- und Schubfeldversuchen untersucht. Sandwich panels as bracing diaphragm and load bearing wall. Traditionally, are structural components for wall cladding and roof covering of a building. They are mounted on a load-bearing substructure. Thus, they are considered as secondary structural component of a building and are classified as self-supporting structural members. Statically, they act as single or multi span beams. They transfer self-weight and external loads from wind and snow to the substructure. Only bending moments and shear forces occur. When the conventional bracing members are missing, the sandwich elements are subjected additionally to loads in the plane of the panel. On the one hand they serve in vertical direction as load bearing wall, on the other hand they stabilize the building against horizontal loads. This load-bearing behaviour was investigated in axial load and wall racking tests at iS-mainz.

Objective To evaluate the effects of valgus knee bracing on pain and function, and compliance and complications, in patients with medial knee osteoarthritis (OA). Methods A meta-analysis of randomized controlled trials that compared changes in patient-reported pain and/or function in patients with medial knee OA was performed. Seven databases were searched from their inception to January 2014. Two reviewers independently determined study eligibility, rated risk of bias, and extracted data. Pooled estimates and 95% confidence intervals (95% CIs) for standardized mean differences (SMDs) for the improvement in pain (and function) were calculated. Event rates (proportions) were calculated for studies that reported complications. Results Six studies were included in the meta-analysis. Overall, there was a statistically significant difference favoring the valgus brace group for improvement in pain (SMD 0.33 [95% CI 0.13, 0.52], P = 0.001) and function (SMD 0.22 [95% CI 0.02, 0.41], P = 0.03). When compared to a control group that did not use an orthosis, the effect size was moderate for pain (SMD 0.56 [95% CI 0.03, 1.09], P = 0.04) and function (SMD 0.48 [95% CI 0.02, 0.95], P = 0.04). When compared to a control group that used a control orthosis, only a small, statistically significant effect for pain remained (SMD 0.33 [95% CI 0.08, 0.58], P = 0.01). Instructions for brace use varied considerably and compliance ranged from 45% to 100%. Up to 25% of patients reported minor complications with brace use. Conclusion Meta-analysis of randomized trials suggests valgus bracing for medial knee OA results in small-to-moderate improvements in pain. Effect sizes vary based on study design and warrant future research.

Summary Steel shear panels in combination with bracing are a novel form of steel shear walls that eliminate large distributed loads to impose on primary beams along with columns. This paper presents the results of a comparative experimental program on two types of steel shear panels with and without stiffeners. For this purpose, the proposed quasi-static cyclic loading history of Federal Emergency Management Agency(FEMA) 461 was applied on two full-scale specimens. Structural steel was selected as the material of the panels, which were welded to the surrounding boundary elements. In addition, using finite element models, performed tests were simulated and scaling effects were investigated. This study identified that steel shear panels have acceptable hysteretic behavior in addition to excellent ductility, which cause more dissipation of induced seismic energy. Comparison of seismic performance of two types of steel shear panels and high cost of setting up stiffeners demonstrate that unstiffened shear panel is a reliable selection for seismic-resisting systems. The results of numerical study show that acceleration-based similitude laws have acceptable estimation for responses of scaled models. Copyright © 2015 John Wiley & Sons, Ltd.

Valgus unloader braces are a conservative treatment option for medial compartment knee osteoarthritis that aim to unload the damaged medial compartment through application of an external abduction moment. Patient response to bracing is highly variable, however. While some experience improvements in pain, function, and joint loading, others receive little to no benefit. The objective of this work was to analyze clinical measures and biomechanical characteristics of unbraced walking to identify variables that are associated with the mechanical effectiveness of valgus unloader bracing. Seventeen patients with medial knee osteoarthritis walked overground with and without a valgus unloader brace. A musculoskeletal model was used to estimate the contact forces in the medial compartment of the tibiofemoral joint and brace effectiveness was defined as the decrease in peak medial contact force between unbraced and braced conditions. Stepwise linear regression was used to identify clinical and biomechanical measures that predicted brace effectiveness. The final regression model explained 77% of the variance in brace effectiveness using two variables. Bracing was more effective for those with greater peak external hip adduction moments and for those with higher Kellgren-Lawrence grades, indicating more severe radiographic osteoarthritis. The hip adduction moment was the best predictor of brace effectiveness and was well correlated with several other measures indicating that it may be functioning as a "biomarker" for good bracing candidates. Clinical significance The ability to predict good candidates for valgus bracing may improve issues of patient compliance and could enable the ability to train patients to respond better to bracing. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:351-356, 2018.

SUMMARY A damper system that absorbs energy over a wide range of displacement amplitudes during building vibration was proposed. This system uses a serial connection of a metallic yielding component and viscoelastic damper with a displacement limit mechanism. Three types of the system were developed and tested: a diagonal bracing type, inverted V bracing type, and wall type. The test results showed that all these systems have damping ratios higher than 8% at small vibration amplitudes on the order of 0.1 mm. For a large vibration, a displacement limit mechanism with two pins limited the displacement of the viscoelastic damper as designed. Analytical simulations established that the system reduced the acceleration and the story drift to 60–70% and 80%, respectively, during a small earthquake compared with a conventional metallic yielding damper system. Furthermore, it showed an equivalent control performance during a severe earthquake. The damper system requires that a clearance be maintained for the displacement limit mechanism. However, this may be lost through construction error, residual displacement after an earthquake, and temperature effects. The changes in the clearance due to these effects were discussed. Copyright © 2014 John Wiley & Sons, Ltd.

Summary In physical theory models, the hysteretic response of concentric braces is simulated by modelling the bracings with two nonlinear fibre-section beam–column elements connected together with an initial out-of-straightness imperfection (∆0). The width of such imperfection is the parameter governing the numerical prediction of the brace buckling. In this paper, the accuracy of different formulations of ∆0 is investigated and validated against monotonic and cyclic experimental results from literature carried out on different bracing configurations. Correlations and measures of scatter between the predicted response and experimental performance are evaluated. A statistical analysis on both X-braced and inverted-V-braced frames based on Monte Carlo simulation is presented and discussed for the following reasons: (a) in order to account for the dispersion of the nonlinear dynamic-evaluated seismic performance due to epistemic uncertainties associated with examined formulations for camber width and (b) to provide modelling correction factors of simulated interstorey drift demand. The analysis shows that the formulations used for ∆0 affect the drift demand, the collapse mechanism and have a noticeably impact on the seismic response parameters at collapse. In particular, inverted-V-braced frames are more influenced than X-braced configurations, because the prediction of brace–beam interaction is very sensitive to ∆0. Copyright © 2014 John Wiley & Sons, Ltd.

SUMMARY Passive structural control techniques are generally used as seismic rehabilitation and retrofit methodologies for existing structures. A poorly explored and exciting opportunity within structural seismic control research is represented by the possibility to design new structural forms and configurations, such as slender buildings, without compromising the structural performance through an integrated design approach. In this paper, with reference to viscous dampers, an integrated seismic design procedure of the elastic stiffness resources and viscoelastic properties of a dissipative bracing-damper system is proposed and developed to ensure a seismic design performance, within the displacement-based seismic design, explicitly taking into account the dynamic behaviour both of the structural and control systems. The optimal integrated seismic design is defined as the combination of the variables that minimizes a suitable index, representing an optimized objective function. Numerical examples of the proposed integrated cost-effectiveness seismic design approach both on an equivalent SDOF system and a proportionally damped MDOF integrated system are developed defining the design variables, which minimize the cost index. Validation of the effectiveness of the proposed integrated design procedure is carried out by evaluating the average displacement of the time-history responses to seven unscaled acceleration records selected according to EC8 provisions. Copyright © 2014 John Wiley & Sons, Ltd.

SUMMARY This paper determines the seismic performance of four-storey concentrically braced frames equipped with either steel buckling-restrained braces or buckling-restrained superelastic shape memory alloy (SMA) braces through incremental dynamic analysis. The incremental dynamic analysis technique is used to examine the behaviour of four-storey braced frames with four different bracing configurations (including diagonal, split-X, chevron-V and inverted-V) under 20 different ground motion records. The study reveals a satisfactory performance at the design intensity level for both types of braced frames. The results show that the SMA braces lead to a uniform distribution of inelastic response over the height of the buildings, as well as mitigating seismic response in terms of maximum inter-storey drift and residual roof displacement. By comparing the responses of SMA and buckling-restrained braced frames under higher intensities of earthquake loading, it is found that the SMA braces can be more beneficial especially under severe ground motion excitations. Copyright © 2014 John Wiley & Sons, Ltd.

SUMMARY Substructure hybrid simulation has been the subject of numerous investigations in recent years. The simulation method allows for the assessment of the seismic performance of structures by representing critical components with physical specimens and the rest of the structure with numerical models. In this study the system level performance of a six-storey structure with telescoping self-centering energy dissipative (T-SCED) braces is validated through pseudo-dynamic (PsD) hybrid simulation. Fragility curves are derived for the T-SCED system. This paper presents the configuration of the hybrid simulation, the newly developed control software for PsD hybrid simulation, which can integrate generic hydraulic actuators into PsD hybrid simulation, and the seismic performance of a structure equipped with T-SCED braces. The experimental results show that the six-storey structure with T-SCED braces satisfies performance limits specified in ASCE 41. Copyright © 2013 John Wiley & Sons, Ltd.

The purpose of this study was to examine the effects of ankle bracing on knee kinetics and kinematics during volleyball tasks. Fifteen healthy, elite, female volleyball players performed a series of straight-line and lateral volleyball tasks with no brace and when wearing an ankle brace. A 14-camera Vicon motion analysis system and AMTI force plate were used to capture the kinetic and kinematic data. Knee range of motion, peak knee anterior-posterior and medial-lateral shear forces, and peak ground reaction forces that occurred between initial contact with the force plate and toe off were compared using paired sample t-tests between the braced and non-braced conditions (P < 0.05). The results revealed no significant effect of bracing on knee kinematics or ground reaction forces during any task or on knee kinetics during the straight-line movement volleyball tasks. However, ankle bracing was demonstrated to reduce knee lateral shear forces during all of the lateral movement volleyball tasks. Wearing the Active Ankle T2 brace will not impact knee joint range of motion and may in fact reduce shear loading to the knee joint in volleyball players.

SUMMARY The usage of special materials with unique properties in seismic resistant structures has increased since the 1994 Northridge earthquake to overcome limited energy dissipation and ductility. Among them, shape memory alloy (SMA) is a unique metallic alloy that has the ability to undergo large deformations and revert back to its original un-deformed shape. Thus, a simple and practical hybrid damping device equipped with SMA that provides both energy-dissipating and re-centering (strain-recovering) capabilities is developed and evaluated in the present paper. Quasi-static loading tests on Nitinol bars are conducted to obtain their mechanical properties in tension and compression. The optimum proportion of SMA and steel in the device is achieved through analyzing various models. Placing the proposed device in semi-rigid bracing members of special structures will localize the energy-dissipating and ductility while providing the brace with strain-recovering capability. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY Performance-based design method, particularly direct displacement-based design (DDBD) method, has been widely used for seismic design of structures. Estimation of equivalent viscous damping factor used to characterize the substitute structure for different structural systems is a dominant parameter in this design methodology. In this paper, results of experimental and numerical investigations performed for estimating the equivalent viscous damping in DDBD procedure of two lateral resistance systems, moment frames and braced moment frames, are presented. For these investigations, cyclic loading tests are conducted on scaled moment resisting frames with and without bracing. The experimental results are also used to calibrate full-scale numerical models. A numerical investigation is then conducted on a set of analytical moment resisting frames with and without bracing. The equivalent viscous damping and ductility of each analytical model are calculated from hysteretic responses. On the basis of analytical results, new equations are proposed for equivalent viscous damping as a function of ductility for reinforced concrete and steel braced reinforced concrete frames. As a result, the new equation is used in direct displacement-based design of a steel braced reinforced concrete frame. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY This paper addresses the seismic retrofit of the University of California at Berkeley's California Memorial Stadium (CMS) to accommodate surface fault rupture movements as well as intense seismic shaking from the Hayward fault. For the surface fault rupture aspect of the project, the project team took a multidisciplinary approach that involved structural engineers, geotechnical engineers, seismologists and geologists collaborating to establish design criteria and possible surface rupture scenarios. The mechanics of surface fault rupture are discussed relative to the structural design approach that mitigates the effects of surface deformations caused by the fault during an earthquake. The effects of the surface fault rupture were studied using small scale physical models and nonlinear finite element models of the building and rupturing ground surface. The retrofit scheme accommodates the concentrated ground deformations of an estimated 6 ft of horizontal movement and 2 ft of vertical offset caused by a surface fault rupture. Segments of the CMS that overlay the regions of possible surface fault rupture were decoupled from the main structure via movement gaps to accommodate relative displacements of the building segments, including tilting in the event of earthquake-produced fault rupture. The results of the analyses are discussed along with the design decisions and challenges of retrofitting a historic structure that resides on an active fault. While a large portion of the engineering effort was devoted to solving the issue of accommodating surface rupture, another large engineering challenge also dominated the design of the CMS. One of the signature architectural features of the stadium is a two-story, 375-ft long press box that hovers above the new west side of the seating bowl. Although designing the press box on limited supports to give the appearance of ‘hovering’ was a challenge, the real challenge came in safely bracing this structure for large potential ground motions at this site. The interface between the flexible support of the press box and the rigid seating bowl became a challenge, solved by providing a separation between the bowl and press box structures allowing them to move independently while linking them only with fluid viscous dampers. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY Vibration control systems are being used increasingly worldwide to provide enhanced seismic protection for new and retrofitted buildings. This paper presents a new vibration control system on the basis of a seesaw mechanism with viscoelastic dampers. The proposed vibration control system comprises three parts: brace, seesaw member, and viscoelastic dampers. In this system, only tensile force appears in bracing members. Consequently, the brace buckling problem is negligible, which enables the use of steel rods for bracing members. By introducing pre-tension in rods, long steel rods are applicable as bracing between the seesaw members and the moment frame connections over some stories. Seesaw mechanisms can magnify the damper deformation according to the damper system configuration. In this paper, first, the magnification factor, that is, the ratio of the damper deformation to the story drift, is delivered, which includes the rod deformation. Results of a case study demonstrate that the magnification factor of the proposed system is greater than unity for some cases. Seismic response analysis is conducted for steel moment frames with the proposed vibration control system. Energy dissipation characteristics are examined using the time-history response results of energy. The maximum story drift angle distributions and time-history response results of displacement show that the proposed system can reduce the seismic response of the frames effectively. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY Semi-rigid connections are widely used in different countries. These connections are usually used in semi-rigid frames with bracing system. Considering the frequent use of these connections, studying their behavior as an individual connection or as a frame with a semi-rigid connection is of great importance. In this paper, moment–rotation behavior of bolted angle connection as a usual semi-rigid connection is studied, and the affecting factors on there are investigated. Finite element connection models are developed. These models are verified by comparing the results of finite element analyses with the results of experimental test, and the verified models are used to investigate the behavior of the connections. The behavior of semi-rigid frame with bolted angle connection is then studied conducting time-history analyses. The results show that the increase in shear stiffness of angle bolted connections significantly decreases the lateral drift and increase the frame stability against lateral loading. Copyright © 2012 John Wiley & Sons, Ltd.

Objective To determine the effect of ankle braces on kicking accuracy, speed, and agility in competitive, nonelite soccer players. We hypothesized that the use of ankle bracing would significantly decrease performance in soccer-specific drills immediately after use but not after acclimation to the brace. Design A prospective randomized controlled trial. Setting University. Participants Twenty healthy recreational adult soccer players (5 men and 15 women; mean age, 23 ± 4.8 years) without a history of lower extremity injury in the past 6 months. All the subjects completed the study. Methods The subjects completed a set of performance measures (ie, accuracy shooting at a target, 40-yard dash, S180° run, and T test) with an McDavid 199 Lightweight ankle brace (test subjects) and without an ankle brace (control subjects) during 2 testing sessions spaced 7-10 days apart. Between the 2 testing sessions, the subjects wore the ankle brace on at least 4 occasions while participating in athletic activities to ensure that a learning effect occurred. Main Outcome Measurements Outcomes included kicking accuracy (accuracy shooting at a target) and speed and agility (time to complete a 40-yard dash, S180° run, and T test). Results No significant difference in performance was found for the accuracy in shooting at a target, 40-yard dash, S180° run, and T test ( P > .05) with and without an ankle brace during a session and between sessions. Conclusions Ankle braces did not significantly affect performance in speed, agility, or kicking accuracy in healthy, competitive, recreational soccer athletes.

SUMMARY In order to improve the efficiency of tube-type structures in tall buildings, a new structural system, called hexagrid, is introduced in this paper. In comparison with diagrid system, it consists of multiple hexagonal grids on the face of the building. In this research, a set of structures using diagrid system having four various diagonal angles and hexagrid system were designed on a strength and stiffness-based approach for buildings with 30, 50, 70 and 90 stories to withstand wind load. The impact of different geometric configurations of structural members on the maximum lateral displacement and architectural performance in both diagrid and hexagrid systems is compared. The stiffness sensitivity using a similar interior bracing system in both systems is also discussed. In this study, the seismic performance of a 30-story diagrid structure and a hexagrid structure was evaluated using nonlinear static and dynamic analyses. According to the results, the hexagrid system has a better architectural view and more ductility and stiffness sensitivity, which are about three times than that of the diagrid system. And finally, in comparison with the diagrid system, the hexagrid system has enough potential to push the height limit. The guidelines discussed here are for architectural and structural engineers to improve freehand design. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY In this paper, the seismic behavior of dual structural systems in forms of steel moment-resisting frames accompanied with reinforced concrete shear walls and steel moment-resisting frames accompanied with concentrically braced frames, have been studied. The nonlinear behavior of the mentioned structural systems has been evaluated as, in earthquakes, structures usually enter into an inelastic behavior stage and, hence, the applied energy to the structures will be dissipated. As a result, some parameters such as ductility factor of structure (μ), over-strength factor (Rs) and response modification factor (R) for the mentioned structures have been under assessment. To achieve these objectives, 30-story buildings containing such structural systems were used to perform the pushover analyses having different load patterns. Analytical results show that the steel moment-resisting frames accompanied with reinforced concrete shear walls system has higher ductility and response modification factor than the other one, and so, it is observed to achieve suitable seismic performance; using the first system can have more advantages than the second one. Copyright © 2011 John Wiley & Sons, Ltd.

Single-storey steel buildings in Canada are generally designed with a steel roof deck diaphragm to resist and transfer lateral loads to the vertical bracing system. Current Canadian seismic design provisions for these buildings are reviewed here with a focus on the design of the roof diaphragms. An equivalent static analysis method is generally used for these structures and comprehensive capacity design principles are applied to achieve a proper strength hierarchy in order to develop the intended yielding mechanism along the lateral load path. The method is illustrated with the help of a numerical example. The influence of roof diaphragm in-plane flexibility on the dynamic seismic response is discussed.

In steel construction X-type bracings are very often designed under the assumption that the compression diagonal will go slack and only the tension diagonal is accounted for in the structural analysis. With higher horizontal loads, when heavier diagonal sections are required, this assumption does not hold because the compression diagonal develops a considerable buckling load and thus will contribute to the horizontal stiffness of the bracing. If we look at the dynamic behaviour of such a bracing we will find, that we cannot define a natural frequency in the classical sense, since the stiffness of the system is switching during its cyclic motion. This has also implications on the maximum amplitude which will develop under harmonic excitation. These effects are investigated with realistic cross section of a steel structure; conclusions for practical design are given. Dynamisches Verhalten von Stahlbauten mit Kreuzverbaden. Kreuzverbande in Stahlbauten werden haufig unter der Annahme bemessen, dass die Druckdiagonale schon bei kleinsten Lasten ausfallt. Verschiebungen und Eigenfrequenzen werden dann unter ausschlieslichem Ansatz der Zugdiagonalen ermittelt. Dieser Ansatz kann fur Diagonalen mit Rund- oder Flach-Querschnitten realitatsnahe sein. Wenn grosere Horizontallasten abzutragen sind, wie dies haufig im Anlagenbau der Fall ist, werden z. B. Diagonalen aus Doppelwinkeln gewahlt. Deren aufnehmbare Drucknormalkraft ist nicht mehr vernachlassigbar, so dass der oben beschriebene Ansatz nicht mehr realitatsnah ist. Im folgenden Artikel wird das dynamische Verhalten dieser Verbande genauer untersucht. Anhand eines stahlbautypischen Beispiels, welches einer Veroffentlichung von Celtikci et al. [1] entnommen ist, wird die tatsachliche Arbeitslinie eines Verbandsfeldes mit einem Schaltpunkt und unterschiedlichen inkrementellen Steifigkeiten entwickelt. Die Abschatzungen nach den ublichen ingenieurmasigen Berechnungsverfahren werden einer numerischen Simulation gegenubergestellt. Als Ergebnis wird festgestellt, dass die vereinfachende Abschatzung, bei der nur die Zugdiagonalen angesetzt werden, hinsichtlich der dynamischen Amplituden auf der sicheren Seite liegt.

SUMMARY The results of experimental tests carried out on reinforced concrete (RC) full-scale 2-storey 2-bays framed buildings are presented. The unretrofitted frame was designed for gravity loads only and without seismic details; such frame was assumed as a benchmark system in this study. A similar RC frame was retrofitted with buckling-restrained braces (BRBs). The earthquake structural performance of both prototypes was investigated experimentally using displacement-controlled pushover static and cyclic lateral loads. Modal response properties of the prototypes were also determined before and after the occurrence of structural damage. The results of the dynamic response analyses were utilized to assess the existing design rules for the estimation of the elastic and inelastic period of vibrations. Similarly, the values of equivalent damping were compared with code-base relationships. It was found that the existing formulations need major revisions when they are used to predict the structural response of as-built RC framed buildings. The equivalent damping ratio ξeq was augmented by more than 50% when the BRBs was employed as bracing system. For the retrofitted frame, the overstrength Ω and the ductility µ are 1.6 and 4.1, respectively; the estimated R-factor is 6.5. The use of BRBs is thus a viable means to enhance efficiently the lateral stiffness and strength, the energy absorption and dissipation capacity of the existing RC substandard frame buildings. The foundation systems and the existing members of the superstructure are generally not overstressed as the seismic demand imposed on them can be controlled by the axial stiffness and the yielding force of the BRBs. Copyright © 2011 John Wiley & Sons, Ltd.

In this study, the progressive collapse potential of braced frames was investigated using nonlinear static and dynamic analyses. Eight different bracing types were considered and their performances were compared with those of a special moment-resisting frame designed with the same design load. According to the pushdown analysis results, most braced frames designed per current design codes satisfied the design guidelines for progressive collapse initiated by loss of a first story interior column; however, most model structures showed brittle failure mode caused by buckling of braces and columns. Among the braced frames considered, the inverted-V type braced frames showed superior ductile behaviour during progressive collapse. The nonlinear dynamic analysis results showed that all the braced structures remained in stable condition after sudden removal of a column, and their deflections were less than that of the moment-resisting frame. Copyright © 2009 John Wiley & Sons, Ltd.

Incremental dynamic analysis (IDA) is an emerging method in structural analysis which allows evaluation of seismic capacity and demand of structures through a series of nonlinear dynamic analyses using multiple scaled ground motion records. Seismic behaviour of concentrically braced frames designed based on the first, second and third revisions of the Iranian seismic code, standard no. 2800, has been evaluated through IDA in the present paper. Besides, a brief comparison is made between seismic behaviour of these frames, frames with different heights and different bracing types. Seismic capacity and limit states of such structures have been reviewed through the paper. The IDA results imply that frames designed with the first edition are seriously vulnerable and fail before reaching the acceleration levels predicted in the code. On the other hand, frames designed with the second and third editions, although behaving better, need partial reinforcement in some cases. Other results of this study show that chevron braced frames behave seismically better than X-braced ones. Copyright © 2009 John Wiley & Sons, Ltd.

Structural engineering problems are always affected by many sources of uncertainty, such as aleatory of material properties, applied loads and earthquake intensity, therefore, seismic assessment of structures should be based on probabilistic methods. Since PBSD (Performance-based Seismic Design) philosophy was formulated, many researches have been conducted in this field in order to develop simple and accurate procedures for evaluating structural reliability. An important contribution has been provided by Jalayer and Cornell, who have developed a closed-form expression to evaluate the mean annual frequency of exceeding a defined limit state. In this paper, by assuming the record-to-record variability as the only source of uncertainty, the seismic reliability of concentrically braced frames designed according to traditional and innovative methodologies is investigated, and a comparison between their performances is presented. In particular, two design methodologies have been applied: Eurocode 8 provisions and a new design methodology based on a rigorous application of ‘capacity design’ criteria. The innovative reduced section solution strategy, based on the reduction of cross sections at bracing member ends, has also been analysed. Copyright © 2011 John Wiley & Sons, Ltd.

SUMMARY New closed-form formulae are presented for the torsional analysis of asymmetrical multi-storey buildings braced by moment-resisting (and/or braced) frames, (coupled) shear walls and cores. The analysis is based on an analogy between the bending and torsion of structural systems. A closed-form solution is presented for the rotation of the building. The torsional behaviour is defined by three distinctive phenomena: warping torsion, Saint-Venant torsion and the interaction between the two basic modes. Accordingly, the formula for the maximum rotation of the building consists of three parts: the warping rotation is characterized by the warping stiffness of the bracing system, St Venant rotation is associated with the St Venant stiffness of the building and the third part is responsible for the interaction. It is demonstrated that the interaction between the warping and St Venant modes is always beneficial, as it reduces the rotation of the structure. It is shown how the proposed formula for torsion can be used for the determination of the maximum deflection of multi-storey asymmetrical building structures. The results of a comprehensive accuracy analysis demonstrate the validity of the method. A worked example is given to show the ease of use of the procedure. Copyright © 2010 John Wiley & Sons, Ltd.