The seismic response of steel chevron concentric bracings is significantly influenced by the flexural behaviour of the brace-intercepted beam. The capacity design criteria provided by current codes ...aim both at avoiding the formation of plastic hinge into the beam following the brace buckling and at guaranteeing the energy dissipation by yielding in tension of the brace. However, besides the strength, the beam flexural stiffness has a key role in order to assure the formation of such failure mechanism. Indeed, structures with strong and deformable beams are characterized by poor seismic performance, showing severe damage concentration in the braces under compression, while those in tension behave elastically. In order to investigate this aspect, a comprehensive numerical parametric study is presented and described in this paper. In particular, the influence of beam flexural stiffness on chevron concentric bracings is analysed ranging the ratio between the beam flexural stiffness and the braces vertical rigidity, the beam span, the interstorey height and the brace slenderness. Analytical equations based on the regression of numerical data have been proposed as design aid in order to select the optimal beam stiffness depending on both the required brace ductility and interstorey drift ratio.
•The seismic behaviour of chevron braced frames is investigated.•A numerical parametric study has been carried out.•The influence of the beam stiffness on the overall response is studied.•Empirical equations to estimate brace ductility and beam stiffness are provided.•Design criteria have been proposed to improve the response of chevron braced frames.
In this study performance-based seismic design procedure for staggered truss frames with friction dampers in the vierendeel panels was developed and their seismic performance was evaluated. To this ...end 6- and 12-story analysis model structures with friction dampers were designed using the capacity design procedure. For comparison the same structures without dampers were designed following the strength based approach specified in the ASCE 7–13, and the seismic performances of all model structures were compared. Fragility analyses were carried out to evaluate the seismic safety of the model structures and to validate the response modification factor used for seismic design. Analysis results showed that the capacity design method leaded to the formation of plastic hinges concentrated at vierendeel panels. It was also observed that the substitution of rotational friction dampers at the location of plastic hinges resulted in enhanced ductility and reduced probability of failure when the structures were subjected to design level seismic load.
•Seismic design method of staggered truss frames was developed.•Model structures with friction dampers were designed using the proposed design procedure.•Proposed design method leaded to the formation of plastic hinges concentrated at virendeel panels.•Use of rotational friction dampers resulted in enhanced ductility and reduced probability of failure.
Eccentrically braced frame (EBF) is considered a suitable seismic resisting system in terms of its high ductility, and stiffness simultaneously. In this frame, nonlinear behavior and energy ...dissipation are limited to link beam, and other members (capacity-designed members) are designed in proportion to maximum link shear force. Despite the significance of capacity-designed members, their reliability evaluation and the effect of their failure on the overall behavior of EBF have not been studied in prior research. The aim of this paper is to evaluate the effect of brace failure on the probability of collapse by considering system overstrength, varied ratios of the capacity to demand factors (ϕ/γ) in brace design, and seismic hazard curve. To achieve this aim, Incremental Dynamic Analysis (IDA) was used to study nonlinear structural models of EBF, evaluate the force demands on the braces, and the effects of brace failure on the system collapse. The reliability analysis was performed by integrating the viewpoint of LRDF component design with the FEMA P695 system reliability methodology. The results indicate that the probability of total collapse increases significantly at low spectral acceleration due to brace failure. Additionally, the appropriate value of ϕ/γ in brace design can be calculated for different seismic areas and system overstrength to ensure an acceptable margin of collapse safety.
By analyzing the ductility of two typical failure modes of staggered truss framing systems, it is known that the failure mode of chords failure is better than that of web members failure. In order to ...achieve the expected failure mode, the capacity design principles and a more accurate calculation model are adopted to obtain the axial force demands of truss web members. Then, two 1:2.5-scale truss specimens with different lengths of vierendeel panel were designed, fabricated, and tested under cyclic loadings. The experiment showed that the trusses designed by this method can achieve the expected structural failure mode under lateral force. However, the ductility factors of the specimen SST1 with equal panel length and the specimen SST2 with large vierendeel panel length are 2.91 and 2.47 respectively, which are relatively poor compared with the ordinary moment-frame systems, and increasing the length of the vierendeel panel cannot improve the ductility of truss. Truss specimen with longer vierendeel panel had greater ultimate lateral displacement but lower bearing capacity and initial stiffness. And the analysis showed that the energy dissipation capacity of the two specimens was relatively close, and increasing the length of the vierendeel panel cannot improve the energy dissipation capacity of truss neither.
•A capacity design method was proposed for web members of staggered truss framing systems (STFS).•The test results show that the truss designed by proposed method can achieve the expected failure mode under lateral load.•The test results showed that the ductility factor of truss is lower than that of the ordinary moment-frame systems.•The influence of length of vierendeel panel on the seismic performance of truss is analyzed through the tests.
Capacity design: Early history Fardis, Michael N.
Earthquake engineering & structural dynamics,
November 2018, Letnik:
47, Številka:
14
Journal Article
Recenzirano
Summary
The paper documents the little‐known story behind the development of the concept of capacity design and sheds new light regarding the individual contributions, which led to it becoming an ...important design tool for the control of inelastic response. The basic concept was laid out in the 1961 book by Blume, Newmark, and Corning, Design of Multistory Reinforced Concrete Buildings for Earthquake Motions, with the notable sections written by Mete Sozen; the basic concept was included in the 1967 to 1968 revision of the Structural Engineers Association of California (SEAOC) recommendations. John Hollings, a prominent structural designer in New Zealand, quoted the SEAOC recommendations and Blume, Newmark, and Corning when he used these ideas in a design procedure he proposed in 1968 to 1969 for the control of the inelastic response in concrete buildings. The term “capacity design” for that procedure seems to have been coined by a select team of structural designers of New Zealand's public buildings under the leadership of Otto Glogau, who had already introduced the new SEAOC rules in the 1968 New Zealand design code for public buildings. Tom Paulay is credited with publicizing and further development of capacity design as a holistic approach for the control of inelastic response. He was instrumental in disseminating the concept, especially in Europe, and often is called the “father” of capacity design.
•Force transfer mechanism in bolted I-shape brace connection is studied.•Initial bolt bearing in the flange and web branches is not synchronized.•Significant nonuniform shear force distribution exits ...in the bolt group.•Loading eccentricity of welds is quantified.•Design recommendations are proposed to avoid bolt and weld failure.
In many low and moderate seismic regions, a low-ductility concentrically braced frame (CBF) is used as the seismic force resisting system for steel structures. The design of such CBFs is straightforward: all members and connections are designed based on the seismic force demand obtained through linear elastic structural analysis; capacity-based design and additional seismic detailing are not required. There is no designated energy-dissipating fuse in the lateral load-carrying path. Such CBFs are referred to as Conventional CBFs (CCBFs) in this study. In CCBFs, the brace-to-gusset connections are inherently weaker in tension than the adjoining gusset plates and braces. This occurs because both the gusset plates and the braces are selected on the basis of their respective compressive buckling resistances, and hence, typically have a much greater resistance in tension. Described herein is a numerical study of the popular flange plate bolted I-shape brace connection configuration. A high-fidelity finite element (FE) simulation procedure was developed and validated against laboratory test results. The resulting numerical models were created with the objective of improving our understanding of the inelastic response of these brace connections. The force transfer mechanism within the two branches of the connection was characterized. Significant nonuniform shear distribution was found to exist within the bolt group in the flange branch, which may be detrimental to the safe functioning of these bolts in the seismic design context. The loading eccentricity on the weld group was quantified. Recommendations on how to avoid brittle bolt shear rupture and premature weld fracture are proposed.
•Direct displacement-based design (DDBD) for coupled walls with shear link coupling beams using inelastic displacement spectra.•Capacity design: Continuum model of coupled walls is used for shear ...force and bending moment estimation.•Drift of the coupled walls is restricted within desired limits.•Predicted shear force demands show good accuracy and bending moment demands show moderately good results.
Coupled walls with replaceable steel shear link coupling beams are used to minimize the repair cost and downtime of buildings after major earthquakes. In this study, the direct displacement-based design (DDBD) method for coupled walls with steel shear link coupling beams using inelastic displacement spectra is developed. For capacity design, a continuum model of the coupled walls that accounts for the stiffness degradation due to expected damage in the first mode is adopted, to obtain equations to estimate the shear forces and bending moments generated due to higher modes. The effectiveness of the DDBD design method for coupled walls with steel shear link coupling beams is assessed by comparing the drift demands with nonlinear response history analysis (NLRHA) results and for capacity design purposes the shear force and bending moment profiles obtained from NLRHA are compared with the results obtained from the equations derived in this study and the weighted capacity design (WCD) method. The results obtained for 5-, 10-, and 15-story coupled walls with steel shear link coupling beams, show that the proposed design methodology is suitable to achieve the design objectives.
•Glued-in rod fasteners were used to adapt advanced structural bracing systems into heavy timber buildings.•A capacity-design procedure was developed for seismic applications of braced timber ...frames.•The hybrid timber-steel braced frame exhibited excellent wind and seismic performance.•The testing provided validation of glued-in rod fasteners for capacity protected braced frame connections.•European glued-in rod design procedures were evaluated for applications in North America.
The practical use of high-performance structural steel bracing systems in heavy timber buildings has not previously been explored. This study investigates the design and behavior of a prototype steel beam to column bracing connection to enable the use of friction damping devices, buckling restrained braces (BRBs) and other high-performance braces to create hybrid timber-steel braced frames. Glued-in rods, with and without pre-tensioning, are used to connect the steel and timber elements in the frame. The timber elements and connections are designed to remain elastic using capacity design principles, allowing the frame to behave similarly to comparable steel high-performance braced frames. A test frame incorporating the new hybrid beam to column bracing connection system with a friction brace device was evaluated and validated using a half scale test of a beam-column-brace connection under wind loading and BRB qualification protocol loading. The tests showed that the connections and timber members remained elastic and could accommodate at least two times the design drift at full load. They also showed that pre-tensioning the glued-in rod connections did not affect the global system performance.
•21 system configurations were investigated for three energy supply scenarios.•Six dimensionless energy matching parameters and three matching maps were proposed.•Mathematical relationship between ...the matching parameters and ESR was established.•Values of ESR were compared for different capacity design method and strategy.•A thermodynamic boundary map of ESR was drawn and a survey in China was conducted.
In this research, 21 combined cooling, heating, and power (CCHP) system configurations that are based on gas engine (GE), gas turbine (GT), and microturbine (MGT) are investigated for three different energy supply scenarios: electricity & cooling, electricity & heating, and electricity & cooling & heating. Moreover, six dimensionless energy matching parameters are proposed to quantitatively measure the disparity of load demands. Thereafter, three matching maps for the GE/GT/MGT-based configurations are drawn to acquire direct insight on the energy matching performance between CCHP systems and users. Concurrently, the mathematical relationship between the matching parameters and energy-saving rate (ESR) is established. Moreover, the ESR values of different capacity design methods and operation strategies for the three energy supply scenarios are discussed and compared. The results show that the maximum ESR value is reached when the energy supply and demand achieved the ideal matching. The following electric load strategy (FEL) and the priority-to-providing-electricity capacity design method (PPE) are the better choices for most situations in terms of system design and operation control, respectively. Moreover, a thermodynamic boundary map of the ESR was drawn to intuitively understand the configurations of energy demands from the most suitable CCHP users as well as the boundaries of ESR for different energy supply scenarios. Finally, the survey results of the indigenous CCHP systems that had been conducted to gain insight on the development of these systems in China are presented in this paper.
Dieser Aufsatz befasst sich mit einer verformungsbasierten Bemessung im Holzbau gegenüber Erdbebeneinwirkungen. Nachdem die normativ geregelten Berechnungsverfahren kurz erläutert werden, werden zwei ...unterschiedliche Modelle beschrieben, mit denen das nichtlineare Verhalten aussteifender Wandtafeln für die Anwendung in einer verformungsbasierten Berechnung prognostiziert werden kann. Alternativ zum Vorschlag im aktuellen Entwurf des Eurocode 8 wird ein eigener Ansatz vorgestellt. Anhand von einzelnen Wandtafeln werden die Prognosemodelle verglichen und die Unterschiede aufgezeigt. Anschließend werden an einem zwei‐ und viergeschossigen Referenzgebäude unter Berücksichtigung verschiedener Ausführungskonfigurationen der aussteifenden Wände verformungsbasierte Bemessungen durchgeführt. Es kann gezeigt werden, dass sich eine verformungsbasierte Bemessung sehr robust gegenüber Veränderungen bei den Prognosemodellen verhält und ein hohes Potenzial vorhanden ist, mögliche Reserven in einer Struktur zu aktivieren.
Translation
Application of displacement based seismic design in light‐frame timber construction
This contribution deals with a displacement based seismic design procedure in timber construction. After a short explanation of the calculation methods regulated by standards, two different models are described with which the non‐linear behaviour of bracing elements in timber construction can be predicted to be included in a displacement based seismic design. In addition to the proposal in the current draft of Eurocode 8, an own approach is presented. The models are compared for different configurations of light frame timber shear walls and the differences are shown. Subsequently, displacement based seismic design is carried out on a two‐storey and a four‐storey reference building, taking into account different design configurations of the bracing system. It can be shown that a displacement based seismic design behaves very robustly in relation to changes of the input parameters and that there is a high potential to quantify hidden potentials in terms of deformation capacity in a structure.
