Results Of Nonlinear Dynamic Analyses Research Articles

Analysis of impact of large commercial aircraft on a prestressed containment building

In this paper, the results of nonlinear dynamic analyses of a concrete containment building under extreme loads are presented. The impact of a large commercial B747 airliner is investigated as the extreme load, and a rigid wall impact test is performed using commercial nonlinear finite element codes. The impact forces exerted by the aircraft are verified compared with the time-dependent impact force provided by OECD/NEA (2002), which was calculated based on the so-called Riera method. The rigid wall impact analysis shows that the finite element model of a B747 is appropriate for the purpose of the aircraft crash analysis exposed to the external hazard of “Beyond Design-Basis Events” defined by U.S. Nuclear Regulatory Commission. Finally, the applicability of this methodology is further studied and verified by conducting parametric studies on the critical infrastructures of nuclear power plant containment structures.

Modified fish-bone model: A simplified MDOF model for simulation of seismic responses of moment resisting frames

This paper presents a simplified Multi-Degree-Of-Freedom (MDOF) model through modification of fish-bone model (or generic frame). Modified Fish-Bone (MFB) model is developed through three enhancements: (i) the moment of inertia for half-beams is reduced slightly to modify the assumption of equal rotation at each story joints, (ii) a number of truss elements are inserted to the fish-bone model to simulate flexural deformation of moment frames due to axial elongation and contraction of columns, and (iii) moment–rotation relationship of representative rotational springs is supposed to be bilinear instead of trilinear in order to consider simultaneous yielding at both ends of the beam in moment frames. The proposed model is evaluated with respect to nonlinear dynamic analysis results of three classic moment resisting frames subjected to 94 records of FEMA-440 ground motion data set. Moreover, the adequacy of this model is compared with the fish-bone model and two predictors of nonlinear seismic demand. The statistical study of predicted interstory drift demonstrates the superiority of the proposed model over the fish-bone model and both seismic demand predictors.

Lateral force distribution on base-isolated structures under near-field earthquakes

In the current paper the accuracy of the International Building Code equivalent static method for base-shear distribution is evaluated to determine the response of seismically isolated structures under near-field earthquakes. For this purpose two-, three-, four- and six-storey building models are designed according to the equivalent lateral-response procedure for different elastomeric isolation systems of 2 s, 2·5 s and 3 s for periods of isolated structures and 6%, 8% and 11% for their damping ratio. Different lateral-force resisting systems such as ordinary steel moment frame, ordinary steel concentrically braced frame and ordinary reinforced concrete shear wall are employed as a superstructure and the effects of 13 near-field ground motions on vertical seismic force distribution, and the linear and non-linear properties of isolation systems are investigated. The results of the equivalent static procedure in vertical distribution of base shear are compared with results obtained from dynamic linear and non-linear analysis and the efficiency of their application is studied. Based on linear and non-linear dynamic analysis results of isolated structures, two new formulae are proposed for vertical distribution of base shear for the isolated structures under near field earthquakes. The proposed linear formula is based on the first mode shape of an isolated structure and the non-linear formula follows three first mode shapes which implies contribution of higher modes in more realistic non-linear analyses.

The role of non-linear dynamic soil-foundation interaction on the seismic response of structures

In this paper we provide an overview of recent research work that contributes to clarify the effects of non-linear dynamic interaction on the seismic response of soil-foundation-superstructure systems. Such work includes experimental results of seismically loaded structures on shallow foundations, theoretical advancements based on improved macro-element modeling of the soil-foundation system, examples of seismic design of bridge piers considering non-linear soil-foundation interaction effects, and numerical results of incremental non-linear dynamic analyses. The objective of this paper is to support the concept of a controlled share of ductility demand between the superstructure and the foundation as a key ingredient for a rational and integrated approach to seismic design of foundations and structures.

Nonlinear elastic dynamic analysis of space steel frames with semi-rigid connections

This paper presents a simple effective numerical procedure based on the beam–column method for nonlinear elastic dynamic analysis of three-dimensional semi-rigid steel frames. The geometric nonlinearity is considered by using stability functions and geometric stiffness matrix. An independent zero-length connection element comprising six translational and rotational springs is used to simulate the steel beam-to-column connection. The dynamic behavior of rotational springs is captured through the independent hardening model. The Newmark numerical integration method combined with the Newton–Raphson iterative algorithm is adopted to solve the nonlinear equations. The nonlinear elastic dynamic analysis results are compared with those of previous studies and commercial SAP2000 software to verify the accuracy and efficiency of the proposed analysis.

Role of wall panel connections on the seismic performance of precast structures

Past seismic events, including the 2009 L’Aquila earthquake and the 2012 Emilia earthquake, clearly demonstrated the inadequacy of the current design approach for the connection system of the cladding wall panels of precast buildings. To clarify this problem the present paper investigates the seismic behaviour of a traditional precast structural frame for industrial buildings with a new type of connection system of cladding panels. This system consists of a statically determined pendulum arrangement of panels, each supported with two hinges to the structure, one at the top and one at the bottom, so to have under seismic action a pure frame behaviour where the wall panels are masses without stiffness. Adding mutual connections between the panels, the wall cladding panels become part of the resisting structure, leading to a dual frame/wall system or to a wall system depending on the stiffness of the connections. The seismic behaviour of this structural assembly is investigated for different degrees of interaction between frame and panels, as well as for an enhanced solution with dissipative connections. The results of nonlinear static (pushover) analyses and nonlinear dynamic analyses under recorded and artificial earthquakes highlight the role of the wall panel connections on the seismic behaviour of the structural assembly and show the effectiveness of the dual frame/wall system with dissipative connections between panels.

接合部降伏する鉄筋コンクリート造骨組の地震応答解析

The results of nonlinear dynamic analysis on the seismic response of reinforced concrete moment resisting frames in which beam-column joints are damaged are reported. In the analysis, beam-column joints are modeled with the simplified macro-element of beam-column joints to simulate the nonlinear behavior after the yielding of beam-column joints. The analytical results indicate that yielding of beam-column joints, which occurs in the beam-column joints with low column-to-beam strength ratio, induces the story collapse mechanism. The seismic acceleration levels of collapse are lower than the case of beam-column joints which do not yield.

Seismic Protection of R/C Structures by a New Dissipative Bracing System

Abstract This study presents the results of numerical investigations carried out on a new alternative dissipative bracing system for improving the seismic performance of R/C frames. The proposed system is composed of ductile shear panel and concentric X-braces, and can be used to provide both ductility and stiffness to existing structures. Under seismic actions the braces are expected to remain elastic, while the panel dissipates significant amount of energy by yielding. A simplified model of the bracing system is developed for global analyses of frames. An energy based design procedure for seismic upgrading of frames with ductile shear panel and concentric X-braces is presented. This simplified procedure, based on energy balance concept and nonlinear static analyses, can represent an advantageous approach in preliminary analysis and design stage. Results of nonlinear dynamic analyses performed on a four-story R/C frame designed only for gravity loads show that the proposed bracing system can protect the primary structural elements of the frame preventing them from damage under severe seismic actions.

Seismic Performance of Building Structures with Spatial Variability

In this study the seismic performances of reinforced concrete apartment buildings with Y-shaped plans having central core are investigated. Three types of model structures are designed for each shape depending on the amount of shear partition walls: structures with all shear walls, structures with all columns except the core walls, and structures with shear walls and columns combined. The required amount of concrete is the largest in the all shear wall structures, and decreases as more and more shear walls are replaced with columns. According to nonlinear static and dynamic analysis results, the structures with all shear walls and all columns turn out to have the largest and the smallest strengths, respectively. Index Terms—Seismic performance evaluation, fragility analysis.

Seismic Protection of Steel Frames Using Friction Damper Devices

This study investigates a friction damping bracing system in order to improve the response of steel frames when subjected to severe seismic excitations, beyond the design earthquake. A simplified model describing the behavior of the friction damper device was developed for global analyses of steel frames. Parametric analyses based on numerical simulations were carried out to evaluate the slip force with the aim of minimizing the values of top displacement and hysteretic energy dissipated by the steel frame. The main results of nonlinear dynamic analyses performed on a six-story steel frame incorporating friction damping bracing systems are presented and compared with the response of the unprotected counterpart. The effectiveness of the protection system was also assessed by examining the seismic response of the frame equipped with traditional braces, without friction devices. The results of the numerical investigations showed that the use of the friction damping bracing system caused an increase of the dissipative capacity of the frame, above all for high seismic actions. The plastic deformation concentrated inside the device, protecting the main structural elements from severe damage. The formation of the plastic hinges at the column base was delayed with respect to the unprotected frame. Numerical analyses indicated that the introduction of supplemental damping by using friction devices in steel bracings is very effective for seismic protection of steel frames subjected to severe seismic excitations.

Progressive collapse analysis of steel frames: Simplified procedure and explicit expression for dynamic increase factor

Progressive collapse refers to a phenomenon in which local damage in a primary structural element leads to total or partial structural system failure. When investigating the progressive collapse of structures, nonlinear dynamic procedures lead to more accurate results than static procedures. However, nonlinear dynamic procedures are very complicated and the evaluation or validation of the results can become very time consuming. Therefore, it is better to use simpler methods. For static analyses, the gravity force applied to the removed column bay should be multiplied by a constant factor of two. However, using a constant dynamic increase factor (DIF) is only appropriate for elastic systems. According to the optimal design of structures, the assumption of elastic behavior after column removal is conservative. Thus, it is necessary to establish an expression for DIF that considers inelastic responses. In this paper, a simplified analysis procedure for the progressive collapse analysis of steel structures is presented using the load displacement and capacity curve of a fixed end steel beam. The results of the proposed method are in good agreement with nonlinear dynamic analysis results. Also, the capacity curve, obtained by dividing the accumulated area under the nonlinear static load displacement curve by the corresponding displacement of the column removed point, is used to predict the progressive collapse resistance of the column removed structure. Finally, an explicit expression for the DIF is established for elastic-perfectly plastic and elastic plastic with catenary action behavior.

Erratum to: Seismic fragility assessment of SMA-bar restrained multi-span continuous highway bridge isolated by different laminated rubber bearings in medium to strong seismic risk zones

This study analytically determines the seismic fragility of a three-span continuous highway bridge fitted with laminated rubber bearings and shape memory alloy (SMA) restrainers. Fragility function, which expresses the likelihood of exceeding a damage state conditioned at a given earthquake intensity, has been derived based on SeismoStruct’s nonlinear incremental dynamic analysis results of the bridge subjected to medium to strong earthquake excitation records. A total of 20 excitation records with peak ground acceleration values ranging from 0.45 to 1.07 g, are used in the nonlinear dynamic analysis of the bridge. A 2-D finite element model scheme is used in this study considering nonlinearity in the bridge piers and the isolation bearings. Two types of laminated rubber bearings are used in the bridge system in addition to the SMA restrainers: high damping rubber bearings and lead rubber bearings. The fragility curves are constructed for two bridge components (i.e. piers and isolation bearings), and the system as well. The component fragility curves are combined to evaluate the fragility curves for the entire bridge system at different damage states. The bridge system, for simplicity, considers the bridge deck, isolation bearings with SMA restrainer and bridge piers but excluding the bridge foundations and the abutments. The numerical results show that the failure probability of the bridge system is dominated by the bridge piers over the isolation bearings. Moreover, the inclusion of SMA restrainers in the bridge system exhibits high probability of failure, especially, when the system is isolated with lead rubber bearings.

A performance-based design approach for retrofitting regular building frames with steel braces against sudden column loss

Progressive collapse resistance of existing building structures against sudden column loss may be increased with adequate supply of steel braces. A performance-based design approach for retrofitting regular building frames with steel braces is proposed in this study. The retrofit design approach is developed from the pseudo-static response analysis of an idealized elastic–plastic, single degree-of-freedom system. Analytical relationship between the increment of collapse resistance and structural characteristics is derived to determine the design strength and stiffness of added braces. Accuracy of the proposed approach is verified with incremental dynamic analysis. Also, its application to multi-story buildings is demonstrated with three frame models. Conservative performance is obtained with the design approach, especially for a larger resistance increment. An iterative modification technique is suggested to refine the retrofit design and only a few nonlinear static iterations are required for convergence. Nonlinear dynamic analysis results indicate that the column-loss response of the braced frames is approximated to the performance target and thus the proposed retrofit design approach is feasible for practical applications.

Progressive collapse behavior of rotor‐type diagrid buildings

SUMMARYIn this study, the progressive collapse‐resisting capacities of axi‐symmetric or rotor‐type diagrid structural system buildings were evaluated based on arbitrary column removal scenario. For analysis models, 33‐story buildings with cylindrical, convex, concave and gourd shapes were designed, and their nonlinear static and dynamic analysis results were compared. The effect of design variables such as the number of total stories, slope of diagrids and the location of removed members was also investigated. According to the analysis results, the rotor‐type diagrid structures showed sufficient progressive collapse‐resisting capacity regardless of the differences in shapes when a couple of diagrids were removed from the first story. The design parameter such as building height and the slope of the diagrids did not affect the results significantly as long as they were designed to meet the current design code. Copyright © 2012 John Wiley & Sons, Ltd.

Seismic analysis of sheathing-braced cold-formed steel structures

The seismic behavior of sheathed cold-formed steel (SCFS) structures is characterized by the lateral response of shear walls. Basically, if cold-formed steel (CFS) structures are designed according to the “sheathing-design” methodology, then the seismic behavior of shear walls is strongly influenced by the sheathing-to-frame connections response, characterized by a remarkable nonlinear response and a strong pinching of hysteresis loops. In this paper the results of an extensive parametric non linear dynamic analysis, carried out on one story buildings by means of incremental dynamic analysis (IDA), using an ad hoc model of the hysteresis response of SCFS shear walls, are presented. An extended number of wall configurations has been considered investigating several parameters such as sheathing panel typology, wall geometry, external screw spacing, seismic weight and soil type. Based on IDA results, three behavior factors have been defined, which take into account overstrength, ductility and both overstrength and ductility, respectively. Finally, a design nomograph for the seismic design of single-storey SCFS frame structures developed on the basis of non-linear dynamic analysis results is presented. This last aims to complete a proposal of a design methodology, already presented by the author in the last years.

Use of rotational friction dampers to enhance seismic and progressive collapse resisting capacity of structures

AbstractPassive energy dissipation devices are generally used to reduce structural responses caused by earthquake or wind loads. This study presents combined system of rotational friction dampers connected to high strength tendons to enhance both seismic and progressive collapse‐resisting capacity of existing structures. Friction dampers were designed using the capacity spectrum method to satisfy given performance objectives against seismic load, and their seismic‐ and progressive collapse‐resisting capacities were investigated. According to the nonlinear dynamic analysis results, the structures retrofitted with rotational friction dampers generally satisfied the given performance objectives against seismic load. Both the nonlinear static and dynamic analysis results showed that the progressive collapse potential of the model structures was significantly enhanced as a result of the seismic retrofit. Copyright © 2009 John Wiley & Sons, Ltd.

Effect of near-fault earthquakes with forward directivity on telecommunication towers

In this paper, the effect of pulse-type motions caused by forward directivity that can release huge amounts of energy in a short time period is studied on a telecommunication tower. Since telecommunication towers have longer periods, they are not as affected by seismic forces. Nevertheless, near source earthquakes characterized by high velocity and velocity pulses can change the behavior of these structures. For this reason, a telecommunication tower located near active faults was selected in this study. Considering the probable earthquake magnitude at the site and the distance of the tower from adjacent faults, nine simulated pulses and three near-fault earthquake records with forward directivity are selected and applied to a 3D finite element model of the tower. The results of nonlinear dynamic analysis, i.e., displacements and damage in the tower, indicate that the maximum displacement and drift ratio of the tower under the pulses are obviously affected by the ratio of the structure period to pulse period. When this ratio is decreased and close to 1.0, the maximum displacement and drift ratio are sharply increased and cause large displacements in the tower.

Simplified Procedure for Progressive Collapse Analysis of Steel Structures

Progressive collapse refers to a phenomenon in which a local damage of a primary structural element leads to the failure of partial or whole structural system. To investigate the progressive collapse of structures, nonlinear dynamic procedure leads to more accurate results than static procedures. Nonlinear dynamic procedure is very complicated and the evaluation or validation of its results may be very time-consuming. Therefore using simplified methods are very important. This paper presents a simplified and accurate analysis procedure for progressive collapse analysis of steel structures. The proposed method results show to have good agreement with nonlinear dynamic analysis results. Also, the capacity curve obtained from dividing the accumulated area under the nonlinear static load-displacement curve by the corresponding displacement of the column-removed point is used to predict the progressive collapse resistance of the column-removed structure.

Assessment of RC columns subjected to horizontal and vertical ground motions recorded during the 2009 L’Aquila (Italy) earthquake

In the aftermath of recent earthquakes there has been substantial field evidence demonstrating that the collapse of several existing structures was caused by the effects of the vertical component of seismic ground motions. Such field evidence has not yet been supported by comprehensive analytical assessment and experimental tests. The present work focuses on preliminary analyses of the seismic response of reinforced concrete (RC) members subjected to horizontal (HGMs) and vertical (VGMs) ground motions recorded during the 2009 L’Aquila (Italy) earthquake. Normalised axial loads in beam–columns as well as the peak ground acceleration ratios between horizontal and vertical ground accelerations are emphasised as they are considered parameters of paramount importance for the assessment of structural components and systems subjected to combined horizontal and vertical ground motions (HVGMs). Results of extensive parametric nonlinear dynamic analyses carried out on simplified structural models are discussed in detail. The sample models comprise cantilever RC columns and a two-storey, two-bay plane frame designed for gravity loads. The structural response quantities for the performed analyses are expressed in terms of axial loads, axial deformations, bending moment-axial load interaction and shear demand/capacity ratios. It is found that the variation of axial loads is significant in columns under HVGMs, especially in compression. For values of normalised axial loads ( ν ) corresponding to actual RC columns in framed building structures, e.g., normalised axial load ν > 0.10 , the average increase of the compression load ranges between 174% ( ν = 0.20 ) and 59% ( ν = 0.50 ). For high values of normalised axial loads the computed axial load-bending moment pairs lie beyond the threshold interaction curves and, in turn, the RC members may fail. The shear demand-to-supply ratio is also detrimentally affected by the high fluctuations of axial loads in the columns. Net tensile forces were computed for columns with low-to-moderate axial gravity preload. In multi-storey framed buildings, the response of central columns is significantly affected by the HVGMs. Reliable seismic performance assessment of framed systems requires that combined HGMs and VGMs should be accounted for in the analyses. Further experimental and numerical research is needed to formulate efficient mechanical models to evaluate the shear capacity of structural members of existing RC framed buildings under earthquake loading.

Retrofit of RC frames against progressive collapse using prestressing tendons

SUMMARYThis study investigates the effect of prestressing tendons on the progressive collapse performance of a 6‐ and 20‐story reinforced concrete model structures. According to nonlinear static and dynamic analysis results, the analysis model structures turned out to be vulnerable to progressive collapse caused by sudden loss of a first story column. However, the RC structures reinforced by external prestressing tendons along floor girders showed stable behavior against progressive collapse. The retrofit effect increased as the initial tension and cross‐sectional area of tendons increased. The incremental dynamic analyses showed that the seismic performance of the model structure was also enhanced after the retrofit using tendons. Based on analysis results, it was concluded that the retrofit of existing buildings using prestressing tendons could be effective for increasing both progressive collapse resisting capacity and seismic performance of RC framed structures. Copyright © 2011 John Wiley & Sons, Ltd.