Search

Since the pioneering works conducted by Housner in the 1960s, energy-based seismic design (EBD) has evolved thanks to many researchers. Notwithstanding, it is overshadowed by the force-based design (FBD) approach, and its implementation in seismic codes is currently limited to structures with energy dissipation systems in Japan. The “Vision 2000” report on future design codes identified EBD as a most promising approach towards the paradigm of performance-based design, however. This paper revises key aspects of EBD, particularly how it differs from FBD and displacement-based design (DBD). Important issues to be addressed in the future so as to implement EBD in the seismic design of conventional structures are underlined. New relations between cumulative energy dissipation and maximum displacement for two different restoring force rules—and for two types of ground motions (with and without pulses)—are presented. Furthermore, a simple means of determining the design-value of the ultimate energy dissipation capacity of non-degrading steel components is put forth.

The seismic capacity of buildings is usually studied through separate analysis of two orthogonal directions, then combined using empirical rules. Nevertheless, the three-dimensional nature of seismic action gives rise to interaction among its different components, especially the two horizontal ones, which can cause substantial discrepancy between the actual 3D response and the one obtained by combining uniaxial responses. The present study addresses this problem for waffle-flat-plate (WFP) structures with an irregular layout of columns from the standpoint of energy dissipation capacity. A portion of a WFP prototype structure that was built in Laboratory was subjected, simultaneously, to two horizontal components of a far-field seismic record upon a shake-table. Several shakings of increasing intensity were applied until the collapse of the structure. Afterwards, a numerical model of the specimen was developed and validated with the experimental results. The numerical model was subjected to several sets of ground motions having diverse ratios of energy input from the horizontal components. When the total energy dissipated by the structure through cumulative plastic deformations until failure was obtained for each set of accelerograms, a fairly stable quantity was found to be concentrated within a narrow range of values. Moreover, the specimen subjected to bi-directional seismic loading showed a higher ultimate energy dissipation capacity than under uni-directional loadings.

Prestressed monoblock railway sleepers are concrete elements with almost no reinforcement apart from the prestressing wires, which makes them very sensitive to any stress variation that can induce tensile stresses. In recent years, severe longitudinal cracking has been observed in a number of sleepers in hot regions of Spain, even before these elements were put in service. This work studies the problem while considering the thermal variation as the main factor affecting this cracking phenomenon. A non-linear static load-step analysis is applied on a non-linear finite element model to reproduce the problem and, after its experimental validation, the influence of three design parameters of the sleepers are studied: the nature of concrete aggregates, the dowel thickness, and the dowel material. The results show that all these three parameters may have significant influence on the problem, with the dowel material being the most important parameter. When the dowels are made of a material with a high elastic modulus and a high thermal expansion coefficient, the crack opening induced by a realistic thermal variation can reach significant values and result in longitudinal crack propagation. The changes of humidity are not considered in this study because they are beyond the scope of this work.

Performance-Based Earthquake Engineering (PBEE) aims at designing structures that are able to satisfy multiple target performance levels at different ground motion intensities. The performance levels can be introduced into the overall design process through energy concepts. It is acknowledged that the design of structures protected by control systems such as base isolation or energy dissipation devices can be efficiently optimized by using an energy-based approach. The energy-based design approach incorporated within the probabilistic framework of the performance-based design is a promising design method. In its development, three important energy-based dissipation parameters are critically needed to evaluate, which are the ratio of hysteretic energy to input energy EH/EI, normalized cumulative damage η, as well as the equivalent number of cycles neq. Therefore, this study has taken a comprehensive investigation of these parameters for four hysteretic systems of structures with the vibration period of 0.05s–4s for 7 damping ratios, that is 0.02, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5, and 6 ductility factors, that is 2, 3, 4, 5, 6 and 8. Empirical formulas of predicting the mean values and standard deviations of the energy-based dissipation parameters are proposed as a function of vibration period, damping ratio, and ductility factors. The proposed predictive models can be easily and conveniently used to evaluate the energy-based dissipation parameters in a deterministic and probabilistic manner in the energy-based design in the framework of PBEE.

Summary Shaking table tests were conducted on a scaled reinforced concrete waffle–flat plate structure. It represented a conventional construction design under current building codes in the Mediterranean area. The test structure was subjected to a sequence of four seismic simulations of increasing magnitude. Each simulation was associated with a seismic hazard level characterized by the mean return period PR. The test structure performed well for the simulations associated with PR = 95, 475 and 975 years but collapsed under the maximum considered earthquake of PR = 2475 years. Damage concentrated at column bases, where the maximum chord rotation reached 93% of the ultimate capacity, and at the transverse beams of the exterior plate-to-column connection that failed in torsion. It is shown that most (from 85% to 90%) of the energy input by the earthquake that contributes to damage is dissipated by the plate. The capacity curve of the tested structure estimated from the experimental base shear vs. top displacement relationship allowed us to compute the overstrength (1.4). It is close to the maximum established by European code EN 1998-1 (1.5). Based on a detailed study of the test results, potential updates to current codes and design recommendations are suggested. Copyright © 2015 John Wiley & Sons, Ltd.

Concentric steel braces and brace-type dampers are often applied to the upgrading of reinforced concrete frames subjected to lateral loads. These braces may develop high axial tension forces, and transferring them appropriately to the existing beam–column joints is a key challenge. This paper investigates a solution for connecting the end-plate of the steel brace with the frame, using (1) shear-key plates fixed to the concrete with anchor bolts, and (2) a low friction material inserted between the end-plates and the shear-key plates. The presence of the low friction material impedes the development of tension forces in the anchor bolts and ensures that they are basically subjected to shear forces. This prevents brittle types of failure (concrete cone failure, pull-out/pry-out failure), and results in a reduction of the number of anchors required as well as anchorage height. The efficiency and validity of the proposed brace–frame connection is investigated experimentally by means of shaking table tests conducted on a 3 × 3 × 3 m3 scaled reinforced concrete frame retrofitted with brace-type hysteretic dampers.

This paper shows the acoustic emission (AE) analysis recorded during the loading process of reinforced concrete (RC) structures subjected to bidirectional seismic loadings. Two waffle plates (bidirectional) supported by isolated square columns were tested on a shaking table with a progressive and increasing ground acceleration until the final collapse. Each specimen was subjected to a different loading history. A relevant delay in the beginning of the significant AE energy is observed as the peak value of the ground acceleration increases. Based on this result, a new AE temporal damage index (TDI), defined as the time difference between the onset of the significant AE activity and the onset of the loading that causes this AE activity, is proposed and validated by comparing it with the plastic strain energy released by the concrete, typically used as a reliable damage level indicator. Good agreement was observed for both specimens and seismic inputs., This research was supported by the regional government of Andalucía, Consejería de Innovación, Ciencia y Tecnología, Project TEP-02429, by the Spanish Ministry of Economy and Competitivity, research project reference MEC BIA2017 88814 R and received funds from the European Union (Fonds Européen de Dévelopment Régional).

The city of Lorca (Spain) was hit on May 11th, 2011, by two consecutive earthquakes of magnitudes 4.6 and 5.2 M $$_\mathrm{w}$$ , causing casualties and important damage in buildings. Many of the damaged structures were reinforced concrete frames with wide beams. This study quantifies the expected level of damage on this structural type in the case of the Lorca earthquake by means of a seismic index $$I_{v}$$ that compares the energy input by the earthquake with the energy absorption/dissipation capacity of the structure. The prototype frames investigated represent structures designed in two time periods (1994–2002 and 2003–2008), in which the applicable codes were different. The influence of the masonry infill walls and the proneness of the frames to concentrate damage in a given story were further investigated through nonlinear dynamic response analyses. It is found that (1) the seismic index method predicts levels of damage that range from moderate/severe to complete collapse; this prediction is consistent with the observed damage; (2) the presence of masonry infill walls makes the structure very prone to damage concentration and reduces the overall seismic capacity of the building; and (3) a proper hierarchy of strength between beams and columns that guarantees the formation of a strong column-weak beam mechanism (as prescribed by seismic codes), as well as the adoption of counter-measures to avoid the negative interaction between non-structural infill walls and the main frame, would have reduced the level of damage from $$I_{v}$$ $$\,=\,$$ 1 (collapse) to about $$I_{v}$$ $$\,=\,$$ 0.5 (moderate/severe damage).

This paper addresses two aspects of the behavior of interior reinforced concrete waffle flat plate–column connections under lateral loads: the share of the unbalanced moment between flexure and excentric shear, and the effect of the transverse beams. A non-linear finite element model (benchmark model) was developed and calibrated with the results of quasi-static cyclic tests conducted on a 3/5 scale specimen. First, from this numerical model, the portion γ v of the unbalanced moment transferred by the excentricity of shear about the centroid of the critical sections defined by Eurocode 2 (EC-2) and by ACI 318-11 was calculated and compared with the share-out prescribed by these codes. It is found that while the critical section of EC-2 is consistent with the γ v provided by this code, in the case of ACI 318-11, the value assigned to γ v is far below (about 50% smaller) the actual one obtained with the numerical simulations. Second, from the benchmark model, seven additional models were developed by varying the depth D of the transverse beam over the thickness h of the plate. It was found that the ductility of the connection and the effective width of the plate can respectively be increased up to 50% and 10% by raising D / h to 2 and 1.5.

Dampers are energy-dissipating devices widely applied for new and existing structures in earthquake prone areas. Among the different types of devices, hysteretic dampers are particularly popular due to their simplicity, economy and low cost. Although many studies have focused on ordinary buildings for evaluating the predictive capability of the different intensity measures (IMs), those dedicated to structures with dampers are scarce. The objective of this paper is to evaluate the capability of the most commonly used IMs to predict the seismic response of frame structures with hysteretic dampers, having low-to-moderate height (less than about 12 stories) and low height-to-width aspect ratios (less than approximately 3). To this end, a 6-story reinforced concrete (RC) frame structure designed to fulfill the old Italian seismic codes was retrofitted with hysteretic dampers. The dampers were designed for two different scenarios depending on the distance to the fault (i.e. near and far field ground motions). Two sets of accelerograms, consisting of ordinary and pulse-like near-fault records, are used in the analyses. Modified versions of existing IMs are also proposed, with the intention of improving the correlations between the considered IMs and response quantities.

En este artículo se analizan distintas alternativas para modelar conexiones interiores forjado reticular-pilar de hormigón armado y se propone una solución que con un coste computacional razonable proporcione resultados muy próximos a los experimentales. El modelo propuesto se valida numéricamente con los resultados obtenidos previamente de un ensayo de laboratorio realizado sobre un espécimen a escala 3/5 de la misma tipología estructural, sometido a ensayo cuasi-estático hasta el colapso. Para tal fin, se aplica la teoría avanzada de mecánica no lineal de hormigón armado sobre un modelo tridimensional de elementos finitos en análisis no-lineal: elementos tipo fibra para componentes unidimensionales y tipo capa para los bidimensionales. Los resultados principales de la simulación fueron: a) la obtención de la curva de capacidad mediante un análisis de empuje incremental (push-over) con control de desplazamientos; b) las curvas histeréticas en la losa, y c) los patrones de fisuras, logrando una concordancia revelada con los resultados experimentales. Several approaches are investigated to model interior reinforced concrete waffle-flat-plate-column connections. A model is proposed that provides very good results with reasonable low computational cost. The proposed model is validated with the experimental results obtained on a 3/5 scale specimen, subjected to quasi-static in cyclic loads up to collapse. To this end, the non-linear advanced theory of reinforced concrete is applied on a three-dimensional finite element model and non-linear analysis are conducted. Both fiber and layer elements are used for the one-dimensional and bi-dimensional components respectively. The main results of the simulation were: (i) the capacity curve obtained through out a push-over analysis with displacement control, (ii) the hysteretic curves of the slab, and (iii) the crack patterns. A very good agreement is found between numerical and experimental results.