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A full-scale, two-tiered steel buckling-restrained braced frame (BRBF) was tested to evaluate experimentally the seismic behavior of steel multitiered BRBFs, namely, column stability response, column seismic demands, and tier deformations under a loading protocol representing earthquake ground motions. The test specimen consisted of diagonal braces oriented in opposing directions in the two adjacent tiers to create the most critical multitier response. The test frame was designed in accordance with the 2010 AISC Seismic Provisions as a lateral load-resisting system of a single-story building. The frame was subjected to a three-phase loading protocol consisting of lateral displacement time histories corresponding to a far-field ground motion record and a near-field ground motion record applied sequentially achieving total frame drifts in excess of 3.5%, followed by a final monotonic lateral displacement corresponding to 4.5% story drift. The test frame exhibited a stable response despite a non-uniform distribution of frame inelastic deformation between the tiers, which induced significant in-plane bending moments in the columns. Flexural bending, combined with a large axial compression force, led to partial yielding in the columns. Large deformation demands were also observed in the BRB yielding in tension and attracting the majority of frame lateral deformation. On the basis of test results, a displacement-based analysis approach was proposed to relate column in-plane bending and flexural stiffness to relative inelastic tier deformations. [ABSTRACT FROM AUTHOR]

This paper presents finite element (FE) investigations of the seismic response of a bridge incorporating a base rocking steel pier. The pier consists of a circular steel tube, circular end plates, posttensioned (PT) tendon(s), and supplemental energy dissipation devices, and is configured to rock at its interface with the foundation. The main characteristic of such a pier is its ability to ensure small residual drifts after undergoing inelastic deformations during cyclic loading. The system has a tendency to close the gap due to the presence of superstructure dead load (DL) and tendon posttensioning force. Using experimental data, the calibration of the FE procedure is done at the material, component, and global system levels. The FE model of a prototype bridge is developed with the rocking pier modelled by continuum elements while superstructure, bearing units, abutment walls and backfill material modelled by discrete elements. The analysis procedure includes the application of one or two earthquake excitations, traffic loads, and braking force. The varied parameters are the diameter‐to‐thickness ratio of the column, presence of a PT tendon, addition of supplemental energy dissipaters (EDs), base plate dimensions, height of ED chairs, and ED strength. The results of dynamic FE studies demonstrate that a bridge utilizing such a pier has the potential to undergo consecutive earthquakes without sustaining significant damage and return to its original position without requiring abutment component stiffness and strength. [ABSTRACT FROM AUTHOR]

The seismic performance of structures could be enhanced by the inclusion of supplemental components that dissipate the earthquake-induced energy. This is especially crucial for rocking structures that possess low energy dissipation properties due to their damage avoidance mechanism. Amongst variously developed yielding-type energy dissipaters (EDs), buckling-restrained energy dissipating carbon steel bars have received considerable attention as they make the most use of the inherent energy dissipation of steel and are easy to fabricate. However, maintenance, repair costs, and performance disruptions owing to corrosive environments have been mostly disregarded in past investigations. Employing stainless steel can be a viable solution to overcome such issues. The work described in this two-part study sheds light on various aspects of the buckling-restrained stainless steel EDs through experimental and finite element (FE) investigations. The mechanical properties of type 304L stainless steel including uniaxial monotonic response, strain sensitivity, and cyclic hardening are characterized. It is shown that the material possesses high ductility along with substantial hardening characteristics. In the first phase of testing, energy dissipating bars with different fuse diameters and lengths are designed. Load and strain capacities and bar-tube interactions of the buckling-restrained energy dissipation device are studied through quasi-static tests. In the second phase of testing, various EDs are designed, fabricated with stainless and mild steel, and tested under quasi-static loading to validate the findings of the FE investigations. The test results demonstrate a stable hysteresis response of the buckling-restrained stainless steel EDs with a cyclic average strain capacity of 10%. The FE modelling procedure, calibration, and parametric studies are presented in the companion paper as Part II. [ABSTRACT FROM AUTHOR]

This article examines the use of rocking steel braced frames for the retrofit of existing seismically deficient steel building structures. Rocking is also used to achieve superior seismic performance to reduce repair costs and disruption time after earthquakes. The study focuses on low-rise buildings for which re-centring is solely provided by gravity loads rather than added post-tensioning elements. Friction energy dissipative (ED) devices are used to control drifts. The system is applied to 2-storey and 3-storey structures located in 2 seismically active regions of Canada. Firm ground and soft soil conditions are considered. The seismic performance of the retrofit scheme is evaluated using nonlinear dynamic analysis and ASCE 41-13. For all structures, rocking permits to achieve immediate occupancy performance under 2% in 50 years seismic hazard if the braces and their connections at the building's top storeys are strengthened to resist amplified forces due to higher mode response. Base shears are also increased due to higher modes. Impact at column bases upon rocking induces magnified column forces and vertical response in the gravity system. Friction ED is found more effective for drift control than systems with ring springs or bars yielding in tension. Drifts are sufficiently small to achieve position retention performance for most nonstructural components. Horizontal accelerations are generally lower than predicted from ASCE 41 for regular nonrocking structures. Vertical accelerations in the gravity framing directly connected to the rocking frame are however higher than those predicted for ordinary structures. Vertical ground motions have limited effect on frame response. [ABSTRACT FROM AUTHOR]

This paper presents two analysis methods for the in-plane seismic response of steel multitiered braced frames (MT-BFs) with three or more tiers: (1) a substructuring technique; and (2) a stiffness analysis method. Both methods are consistent with the 2010 AISC Seismic Provisions and have been developed to estimate column flexural demands and tier drifts to prevent column instability and to mitigate concentration of tier drifts as well as premature brace failure under seismic loading. Both methods account for the progression of brace tension yielding along the frame height as observed in MT-BFs. The substructuring technique is simpler and is limited to regular frames, as it assumes a predefined yielding sequence. The stiffness analysis-based method is more rigorous and can predict the actual frame nonlinear response. It can be applied to both regular and irregular MT-BF configurations. The application of the methods is illustrated for two five-tiered special concentrically braced frame examples. Nonlinear response history analysis is performed to validate the proposed methods for the frames studied. [ABSTRACT FROM AUTHOR]

Multitiered steel concentrically braced frames (CBFs) are commonly used to provide lateral resistance for tall single-story commercial, performing arts, sports, and industrial buildings. The seismic response of these frames is studied in this paper. A set of seven special concentrically braced frames (SCBFs), ranging from 9 to 30 m tall with two to six tiers, located in a high seismic area was designed according to the 2010 AISC Seismic Provisions. Fundamental behavior of the two- and four-tiered frames was investigated using three-dimensional (3D) finite element models with shell elements, with particular focus on the buckling response of the columns. The seismic frame response and column stability were then studied more broadly for all frames using more computationally efficient 3D finite element models with fiber-based beam-column elements, which were validated against the shell element models. Multitiered CBFs designed according to current multistory CBF procedures are shown to develop drift concentration in a single tier and high in-plane column bending demand, which in some cases leads to flexural yielding and column instability. As potential solutions to this problem, alternate design strategies were studied and their seismic performance is also presented. Designing for higher seismic forces did not appreciably improve column stability, but use of fixed column bases or buckling-restrained braces provided improved distribution of drift over multiple tiers and reduced the occurrence of column instability. Unlike multistory braced frame seismic design, column flexural demands are more important in multitiered braced frames and must be considered in seismic design. [ABSTRACT FROM AUTHOR]

This article investigates the seismic design and response of steel multi-tiered concentrically braced frames (MT-BFs) in which braces meet at columns between diaphragms. The seismic design provisions of CSA S16-14 are described and illustrated for three-tiered Type MD (moderately ductile) and five-tiered Type LD (limited ductile) braced frames. Analysis methods are proposed to evaluate the in-plane flexural demand on columns. The seismic response of the frames is examined through nonlinear response history analysis. As assumed in design, inelastic deformations tend to concentrate in one tier over the frame height, causing non-uniform drift demands and in-plane bending moments in the columns. CSA S16 provisions predicted well the frame in-plane flexural response and result in acceptable ductility demands on the braces. An extended seismic analysis and design approach that accounts for vertical distribution of brace tension yielding along the frame height is proposed for frames that exceed the limits prescribed in CSA S16. [ABSTRACT FROM AUTHOR]

A period-independent approach for the selection and scaling of ground motion records aimed at reducing demand variability is proposed for seismic response history analysis. The same set of scaled records can be used to study various structures at the same site regardless of their dynamic characteristics. The statistical robustness of the proposed and current approaches is compared through nonlinear inelastic dynamic analyses performed on single-degree-of-freedom systems and multi-story braced frames. The proposed approach leads to consistent response predictions with a limited number of records. This is advantageous for day-to-day structural design or assessment against code hazard-based seismic demand levels. [ABSTRACT FROM AUTHOR]

The effects of accidental eccentricity on the seismic response of four-storey steel buildings laterally stabilized by buckling restrained braced frames are studied. The structures have a square, symmetrical footprint, without inherent eccentricity between the center of lateral resistance (CR) and the center of mass (CM). The position of the bracing bents in the buildings was varied to obtain three different levels of torsional sensitivity: low, intermediate and high. The structures were designed in accordance with the seismic design provisions of the 2010 National Building Code of Canada (NBCC). Three different analysis methods were used to account for accidental eccentricity in design: (1) Equivalent Static Procedure with static in-plane torsional moments assuming a mass eccentricity of 10% of the building dimension (ESP); (2) Response Spectrum Analysis with static torsional moments based on 10% of the building dimension (RSA-10); and (3) Response Spectrum Analysis with the CM being displaced by 5% of the building dimension (RSA-5). Time history analyses were performed under a set of eleven two-component historical records. The analyses showed that the ESP and RSA-10 methods can give appropriate results for all three levels of torsional sensitivity. When using the RSA-5 method, adequate performance was also achieved for the low and intermediate torsional sensitivity cases, but the method led to excessive displacements (5-10% storey drifts), near collapse state, for the highly torsionally sensitive structures. These results support the current provisions of NBCC 2010. [ABSTRACT FROM AUTHOR]

• Multi-axis pseudo-dynamic hybrid simulation is developed to evaluate seismic stability of steel braced frames. • Advanced hybrid testing system used to perform hybrid simulation is introduced. • Strategies are proposed to overcome challenges associated with hybrid simulation. • Hybrid simulation of two two-tiered steel concentrically braced frame case studies are presented. This paper presents the development and application of multi-axis pseudo-dynamic hybrid simulation for evaluating the seismic stability of steel braced frame structures. The advanced hybrid testing system used to perform hybrid simulation is first described, followed by the development of hybrid simulation and main challenges, namely the friction forces generated in the testing system and high-frequency noise in force feedback signals. The strategies proposed to overcome these challenges are then described. Two pseudo-dynamic hybrid simulations consisting of a two-tiered concentrically braced frame where a full-scale wide-flange column part of the frame is physically tested while the rest of the frame is numerically analysed are finally presented. The test results serve to verify the hybrid simulation technique, evaluate experimentally the seismic stability response of columns of steel multi-tiered concentrically braced frames and validate the findings of past fibre-based numerical models used to assess the seismic response of multi-tiered braced frames. [ABSTRACT FROM AUTHOR]

SUMMARY Controlled rocking steel frames have been proposed as an efficient way to avoid the structural damage and residual deformations that are expected in conventional seismic force resisting systems. Although the base rocking response is intended to limit the force demands, higher mode effects can amplify member design forces, reducing the viability of the system. This paper suggests that seismic forces may be limited more effectively by providing multiple force-limiting mechanisms. Two techniques are proposed: detailing one or more rocking joints above the base rocking joint and providing a self-centring energy dissipative (SCED) brace at one or more levels. These concepts are applied to the design of an eight-storey prototype structure and a shake table model at 30% scale. A simple numerical model that was used as a design tool is in good agreement with frequency characterization and low-amplitude seismic tests of the shake table model, particularly when multiple force-limiting mechanisms are active. These results suggest that the proposed mechanisms can enable better capacity design by reducing the variability of peak seismic force demands without causing excessive displacements. Similar results are expected for other systems that rely on a single location of concentrated nonlinearity to limit peak seismic loads. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This article presents the numerical modeling of large-scale shake table tests of slender 8-story reinforced concrete (RC) shear wall specimens. Nonlinear time history analyses are carried out using reinforced concrete fiber elements (OpenSees, OS) and the finite element (FE) methods (VecTor2, VT2). The effects of the modeling assumptions are investigated, including: (a) the tension stiffening effect, (b) damping, (c) smeared vs. lumped reinforcement, and (d) the use of effective shear stiffness in OS. Good agreements are obtained between the numerical and experimental results. Using the proposed numerical modeling strategy, it is possible to investigate the nonlinear dynamic responses of slender RC wall structures with confidence. [ABSTRACT FROM PUBLISHER]

This paper presents shake table test results on two identical 1:0.429 scaled, 8-story moderately ductile RC shear wall specimens under the expected high-frequency ground motion in eastern North America. The walls were designed and detailed according to the seismic provisions of the NBCC 2005 and CSA-A23.3-04 standards. The objectives were to validate and understand the inelastic responses and interaction of shear and flexure and axial loads in the plastic hinge zones of the walls taking into consideration the higher-mode effects. One specimen was tested under incremental ground motion intensities ranging from 40 to 120% of the design level. The intensity range was increased from 100 to 200% for the second specimen. The response of the walls was significantly affected by the second mode, causing an inelastic flexural response to develop at the base as well as at the sixth level. Dynamic amplification of the base shear forces was also observed in both walls. In the second wall, which was tested in the undamaged condition, peak base shear forces occurred prior to significant inelastic rotation and the contribution to concrete of shear resistance exceeded the value used in the design. Once inelastic rotation had developed that contribution corresponded to the value obtained using a value of 0.18 for the reduction factor accounting for concrete cracking. Inelastic rotation in the upper wall region was found to limit the force demand imposed by the higher-mode response. [ABSTRACT FROM AUTHOR]

An experimental program was undertaken to investigate the inelastic seismic response of metal deck roofing systems. The load carrying capacity of roof diaphragms for low-rise steel buildings, subjected to lateral loads from wind and/or earthquakes, is directly dependent on the performance of the connections. This paper provides information on the cyclic response, including load versus displacement hysteresis and energy absorption capacity of 45 screwed, button punched, and welded side lap connections, for different steel deck types. All of the connections were able to sustain some degree of inelastic response. Typically, welded side lap connections are able to carry the largest shear forces and absorb the greatest amount of energy. [ABSTRACT FROM AUTHOR]

An experimental program was undertaken to investigate the inelastic seismic response of metal deck roofing systems. The load carrying capacity of roof diaphragms for low-rise steel buildings, subjected to lateral loads from wind and/or earthquakes, is directly dependent on the performance of the connections. This paper provides information on the inelastic cyclic response, including load versus displacement hysteresis and energy absorption capacity of 144 deck-to-frame screwed, powder-actuated fastener, and welded connection tests for different steel deck and structure thickness. Powder-actuated fastener connections were able to provide the highest energy dissipation results, followed closely by screwed connections. In many cases, the welded connections exhibited significant ultimate capacities, but failed at small displacements, resulting in low energy dissipation values. However, when welds with washers were used, the ductility and energy absorption ability of the connection were substantially improved. [ABSTRACT FROM AUTHOR]

Recent decades have seen increased interest in using the controlled rocking concept in seismic resisting systems. Unlike conventional systems, where lateral deformation of a member is achieved through the formation of plastic hinges in critical regions, in the rocking systems this is achieved through a gap opening mechanism. Due to gravity load and/or post-tensioning forces, the rocking systems exhibit a self-centering behavior. Conducting a continuum finite element analysis to investigate the seismic response of such a system is quite expensive in terms of computational resources. On the other hand, a simplified macro model using two springs to simulate the gap opening/closing mechanism cannot accurately predict the dynamic response of the system. This study utilizes a multiple-spring model to simulate the nonlinear seismic response of circular tubular steel piers. An efficient optimization procedure based on a genetic algorithm is developed to calibrate the parameters of the springs. The results of continuum finite element analyses are compared with those obtained from the multi-spring model to verify the accuracy of the model. The proposed method is shown to be advantageous for accurately simulating the seismic response of a bridge model subjected to multi-directional ground motions, particularly the hysteretic force-displacement relationship, and dynamic response time history. • Seismic response of posttensioned (PT) rocking steel bridge piers is investigated through continuum and macro finite element (FE) modeling approaches. • Computationally efficient macro modeling approaches, i.e., two and multi -spring macro models, are discussed. • A procedure for calibrating the parameters of the multi-spring model using genetic algorithm is presented. • The performance of two-spring and multi-spring macro models in predicting the seismic response is examined. • Multi-spring macro model is extended to simulated the response of double rocking configuration. [ABSTRACT FROM AUTHOR]

Gravity-controlled rocking braced frames (G-CBRFs) are cost-effective low-damage self-centring lateral force resisting systems that allow the reduction of the seismic force demands in structures subjected to earthquakes, while relying only on the gravity loads they carry to ensure self-centring. Due to column uplift, significant masses are mobilized, thus activating vertical fundamental modes of vibration that affect the overall seismic behaviour of the structures. This article presents an examination of the seismic response of G-CBRF structures, including the response of the roof and floor framing systems. Twenty-two buildings were designed for this study, with various combinations of building heights (2-, 4-, and 8-storeys), building locations (eastern and western Canada), site classes (soil C and E), and location of the braced frame within the building (interior or exterior column lines). For each design, two framing configurations were studied, with secondary beams parallel or perpendicular to the braced frames. Non-linear response history analyses were performed using representative ground motions selected and scaled according to the National Building Code of Canada requirements. Effects of the vertical component of the ground motions and energy dissipated through friction in beam-to-column connections were also of focus. Incremental dynamic analyses were performed to generate fragility curves for collapse due to overturning of the studied structures. The results show that peak drifts can be accurately predicted. Peak axial loads in frame members are increased due to the vertical inertia forces induced upon rocking. The fragility curves show that acceptable margins against collapse by overturning is achieved for G-CRBFs. [Display omitted] • Gravity-controlled rocking braced frames can achieve enhanced seismic performance. • G-CRBFs can demonstrate acceptable margins against collapse by overturning. • Energy dissipation through friction is very effective for controlling storey drifts. • Column uplift and impact trigger vertical response in the adjacent gravity framing. • Floor vibration modes induce significant additional beam shears and moments. [ABSTRACT FROM AUTHOR]