Seismic Details Research Articles

Parametric Analysis on Seismic Performance of Hybrid Precast Concrete Beam‐Column Joint

In this paper, a nonlinear finite element (FE) analysis of high‐performance hybrid system (HPHS) beam‐column connections is presented. The detailed experimental results of the ten half‐scale hybrid connections with limited seismic detailing have been discussed in a different paper. However, due to the inherent complexity of HPHS beam‐column joints and the unique features of the tested specimens, the experimental study was not comprehensive enough. The new connection (HPHS) detail suggested in this study is characterized by ductile connection, steel connectors, and engineered cementitious composite (ECC) which is a kind of high‐performance fiber reinforced cement composite with multiple fine cracks (HPFRCCs). Therefore, in this paper, FE analysis results are compared with experimental results from the cycle tests of the two specimens (RC and PC) to assess model accuracy, and detailed model descriptions are presented, including the determination of stiffness and strength. The critical parameters influencing the joint’s behavior are the axial load on column, beam connection steel plate length, inner bolt stress contribution, and plastic hinge area.

Optimal design algorithm for seismic retrofitting of RC columns with steel jacketing technique

Steel jacketing (SJ) of beams and columns is widely employed as retrofitting technique to provide additional deformation and strength capacity to existing reinforced concrete (RC) frame structures. The latter are many times designed without considering seismic loads, or present inadequate seismic detailing. The use of SJ is generally associated with non-negligible costs depending on the amount of structural work and non-structural manufacturing and materials. Moreover, this kind of intervention results in noticeable downtime for the building. This paper presents a new optimization framework which is aimed at obtaining minimization of retrofitting costs by optimizing the position and the amount of steel jacketing retrofitting. The proposed methodology is applied to the case study of a 3D RC frame realized in OpenSEES and handled within the framework of a genetic algorithm. The algorithm iterates geometric and mechanical parameters configurations, based on the outcomes of static pushover analysis, in order to match the optimal retrofitting solution, intended as the one minimizing the costs and, at the same time, maintaining a specified safety level. Results of the proposed framework will provide optimized location and amount of steel-jacketing reinforcement. It is finally shown that the use of engineering optimization methods can be effectively used to limit retrofitting costs without a substantial modification of structural safety.

Retrofitting RC infills by a glass fiber mesh reinforced overlay and steel dowels: experimental and numerical study

Many existing Reinforced Concrete (RC) buildings infilled with masonry panels are vulnerable to seismic actions due to lack of proper seismic detailing. For buildings located in low-moderate seismicity regions, a possible retrofitting option could be a reinforced mortar coating applied on the building facades in order to significantly increase its seismic resistance. The present paper studies thin glass fiber mesh reinforced mortar overlays for strengthening RC weak frames infilled with hollow brick masonry. Attention is devoted to the steel dowel connection between the masonry panel and the RC frame to reduce shear sliding. An experimental evaluation of the effectiveness of this enhanced technique is presented and compared against previous results in which shear sliding significantly limited the structural response. In addition, a finite element model has been developed and calibrated to properly simulate the response of the test specimens.

Comparative analysis of normative provisions for seismic design and detailing of reinforced concrete structures

Abstract The main objective of this work is to carry out a comparative analysis between the methods and provisions of the Brazilian code ABNT NBR 15421:2006 and those of the ASCE/SEI 7 and the Eurocode 8, on the seismic design of structures. The similarities and differences between these standards, as far as the application of the Equivalent Lateral Forces method (ELFM) and the Response Spectrum method (RSM) are concerned, will be addressed. The responses will be evaluated for a case study that will be modelled by the SCIA Engineer 17 software. This paper also presents some comments on the detailing of reinforced concrete structures to ensure a good performance under seismic loading, allowing for a more favourable interpretation of the seismic analysis results.

Simplified Compression Arch Action Model for R/C Beam-column Assemblages

A set of analytical equations are developed for calculating the beam-column assemblage flexure action capacity and compression arching action capacity under a middle column removal scenario. The suggested equations covered most of the main parameters affecting the assemblage behavior including seismic detailing, longitudinal reinforcement ratios, concrete confinement, and the contribution of concrete flanged slabs. The proposed analytical model for predicting the flexural and compression arching action capacities is validated with a large number of experimental results. The model provides a good estimation for 79 beam-column assemblages with several geometrical, reinforcement configurations, and material parameters. The mean values of the experimental to the theoretical ratio for calculating flexure and compression arching capacities are 1.15 and 1.16, respectively. The predictions of previous compression arch action models are found to be more conservative. Finally, the proposed model is utilized in parametric studies including all key parameters that affected resistance of the beam-column assemblages against progressive collapse.

Structural Assessment and Upgrading for an Old Building Belonging to an Historical Multi-Sports Center in Naples

A significant number of non ductile existing reinforced concrete frame buildings, built in different seismic regions around the world but without adequate seismic detailing requirements, suffered damages or collapse after past earthquakes. In fact, these reinforced concrete frame buildings are much more susceptible to high level of damage or to collapse than modern code-conforming frames. A crucial issue in the community of the earthquake engineering is the assessment and the upgrading of these non ductile reinforced concrete structures. In particular, a careful assessment of the existing building is very important in order to understand the failure mechanisms that govern the achievement of predefined limit states or the collapse of the structure. Only after an in depth seismic assessment, the best upgrading/retrofit strategy can be designed and applied to the structure. In some cases, the historical value of these buildings makes the assessment procedure and the upgrading design more complicated due to the constraints related to the limited possibility of interventions. In this work, a building belonging to an old multi-sports center, is used as case study. The complex orbits around the soccer stadium called Collana and located in Naples. This soccer stadium was initially built in the late '20s and then it was completely rebuilt in the post-war period and used as a sports center for different sporting activities. Currently, the complex includes a soccer field, an athletic track, three indoor gyms, three tennis fields, a medical center sports and the indoor pool building investigated herein. The analysis of seismic vulnerability implemented for the case study building shows an unsafe condition under both static and seismic loads. The building upgrading is provided choosing the best strategy among different options in order to achieve a certain predefined threshold of the seismic safety for the building. Definitively, the paper presents a real upgrading design case study for a building belonging to an historical complex. Assessment and upgrading are shown both based on linear and dynamic non linear analyses procedures. Finally, the effectiveness of the structural interventions of upgrading is measured coherently with the new Italian guidelines for seismic risk classification of construction.

Seismic evaluation of repaired multi-column bridge bent using static and dynamic analysis

Abstract Simulation of the cyclic response of a structurally deficient as-built reinforced concrete three-column bridge bent is conducted. The bent had deficient seismic details and was previously tested under cyclic loads in the field; damage included concrete crushing and longitudinal steel buckling at the column ends. A fiber-based bridge bent model is developed in OpenSees which includes soil-structure interaction (SSI) using simplified springs. The in-situ test of the as-built bent is used to validate the model. Subsequently, the damaged bent is conceptually repaired with a carbon fiber-reinforced polymer (CFRP) enlarged column cross-section, denoted as “CFRP donut”, which includes a CFRP shell, headed steel bars, nonshrink concrete and a steel collar at the column bottom ends; CFRP composite jackets are employed above the CFRP donut to increase column shear and confinement. Design guidelines of the repair using a simplified strut-and-tie model (STM) are presented. A comparison of the as-built and repaired bridge bents under nonlinear static pushover analysis, incremental dynamic analysis (IDA), and fragility analysis using 22 far-field ground motions shows that the repair method is successful.

Seismic Behavior of High-Performance Fiber-Reinforced Cement Composites Beam-Column Connection with High Damage Tolerance

The purpose of this study is to investigate and evaluate the feasibility of using high-performance fiber-reinforced cement composites (HPFRCC) to satisfy the requirement of transverse reinforcement in beam-column joint under seismic loads. The basic mechanical properties of the HPFRCCs are determined by compression, uniaxial tension, and direct shear tests. Four half-scale exterior beam-column connections are cast and tested under cyclic loads. The cracking patterns, hysteresis behavior, ductility, energy dissipation with damping characteristics and joint shear capacity of the HPFRCC beam-column connections are analyzed, investigated, and compared to the cyclic responses of normal concrete connections designed with/without seismic criteria of ACI. The test results revealed that HPFRCC connections considerably enhances shear and flexural capacity and also improved the deformation and damage tolerance behavior in post-cracking stage comparing to normal concrete connections in ultimate stages. Also, the failure mode of HPFRCC specimens changed from shear mode to flexural mode comparing to the connections without seismic details. Severe damages are observed in normal concrete connection designed without considering seismic criteria. Wide diagonal cracking and damage are observed on the designed NC connections under large cyclic displacement at drift 6%. However, in HPFRCC connections, joint remained intact without any cracks and damage until the test end. This implies that the shear stress requirement can be satisfied without any need to the transverse reinforcement in the HPFRCC joint.

Beam-Column Joints Reinforcement Detailing Adequacy in Case of a Corner Column Loss-Numerical Analysis

Abstract This study investigates the behavior of reinforced concrete (RC) beam-column joints at the corner panel after a ground corner column loss scenario. The ductility of a frame is dependent on the ductility of its components, particularly its joints. Deficiency in joints performance can be related to an unexpected event. For example, the removal of a ground corner column turns the joint above into an inverted knee joint, and also inverses the direction of the resulted bending moments in the adjacent exterior and interior joints. Throughout this work, the effects of these changes are evaluated numerically using different modeling techniques considering both seismic and non-seismic reinforcement details. Numerical simulations of standard and sub-standard joints that were verified against experimentally tested joints are also presented. Joint macro models are developed using the OpenSees platform. These numerical models are then used to simulate the substandard beam-column joints appearing in RC frames after ground corner column removal. Moreover, strut and tie models (STMs) were developed for a substandard knee joint to validate the obtained numerical results. The application of the developed numerical models allows to identify the evolution of a joint’s capacity in function of its reinforcement detailing. The analysis shows the suitability of seismic detailing for exterior and interior joints and also a decrease in the inverted knee joint resistance and this can be recovered by adding i) more confinement to the joint panel zone or ii) joint vertical stirrups. An increase in the degree of confidence in the numerical results is achieved by reproduce similar behavior using different analysis methods.

Two-way bending out-of-plane collapse of a full-scale URM building tested on a shake table

This paper describes a shake table test on a one-storey full-scale unreinforced masonry structure, which complements an earlier testing of a two-storey structure with similar characteristics. The building specimen was meant to represent the upper floors of the end-unit of a terraced house, built with cavity walls and without any particular seismic design or detailing. In these specimens, the masonry walls were composed of two leaves: a load-bearing inner one made of calcium silicate bricks sustaining a reinforced concrete floor and an external leaf made of clay-bricks connected to the inner leaf by means of metallic ties. A pitched timber roof was supported by two triangular gable walls. Floor acceleration response histories of the previously tested two-storey specimen were used as input motions. An incremental dynamic test, with vertical and horizontal inputs, was carried out up to the explicit collapse of some bearing elements of the structure. In particular, a two-way bending out-of-plane collapse of a load-bearing wall was observed and described.

Performance Evaluation of Metallic and Synthetic Fiber Hybridization on the Cyclic Behavior of Exterior Beam-Column Joint

Abstract The influence of different fiber profiles and fiber hybridization on the cyclic behavior of an exterior beam-column joint is experimentally studied and compared with conventional specimens. In the beam-column joint, the joint region concrete is substituted with fiber-reinforced concrete (FRC)/hybrid fiber-reinforced concrete (HyFRC) and tested under reverse cyclic loading to examine the inelastic response. The physical properties of composites employed are examined using cylindrical specimens under uniaxial compression. The stress–strain behavior shows tremendous difference in peak and post-peak strength and strain with respect to the volume and type of fibers in the composites. The test results of joint specimens validate that the hybridization of polypropylene fiber with metallic fiber offers better shear resistance and also improves the damage tolerance capacity like high-volume FRC specimens without critical joint detailing. The damping and energy dissipation response of FRC/HyFRC specimens clearly show that the need for seismic detailing can be eliminated using FRC/HyFRC.

Key seismic survey technologies for deep complex geological structures: A case study of the northern section of the Longmenshan Fault Fold Belt in the Sichuan Basin

The northern Sichuan Basin, spreading in the northern section of the Longmenshan Fault Fold Belt, is characterized by dramatic fluctuations in the surface landforms, development of abdominal faults, and low-quality seismic data, resulting in difficulties in clarifying relevant structures. The key target formation, the Mid-Permian Qixia Fm, is deeply buried with thin reservoirs and high heterogeneity, which brings great challenges to seismic prediction. Under such circumstances, researches have been conducted jointly in terms of seismic data acquisition, processing and interpretation, and finally some relevant seismic survey technologies were developed suitable for surface/underground complex structures. Through surface structural surveys, dynamic deep-well lithologic identification, single-point detector deployment and process optimization, acquisition parameters can be excited. In addition, by using an observation system with high-coverage, wide-azimuth and huge-displacement, quality of acquired seismic data can be enhanced dramatically. Seismic imaging technologies for complex structures have been developed to enhance the quality of images for deep formations. These technologies are dominated by microscopic logging-constrained tomography static correction, high-resolution processing with fidelity and amplitude preservation and all-around PSDM in an angular domain. By using high-resolution gravity, magnetic and electric data, details related to geological structures and faults can be identified. In combination with fine seismic data interpretation, structural details and fault features can be verified effectively. Based on forward modeling and fine seismic calibration of reservoirs in individual wells, suitable attributes can be identified for predictions related to the distribution of reservoirs. By using all these auxiliary technologies, a large-scale structural–lithologic composite trap with a total area of 1223 km2 has been discovered in the NW Sichuan Basin. The Shuangyushi–Jiangyou area as a whole distributes on structural highs. In the areas to the south of Shuangyushi, the Qixia Fm dolomite reservoirs of platform margins are continuously developed. In conclusion, these auxiliary technologies can effectively allow trap identification and thin reservoir prediction in complex structures in the study area. In addition to clarifying the exploration orientation and providing a necessarily technical supports for well development, these technologies help to accelerate the construction of demonstration projects for the exploration and development of deep marine carbonate formations.

Deck-pier connection detail for the simple for dead load and continuous for live load bridge system in seismic regions

The steel bridge system referred to as Simple for Dead Load and Continuous for Live Load (SDCL) has gained popularity in non-seismic regions of the United States of America. The system provides enhanced service life and lower inspection and maintenance costs as compared to conventional steel systems. To-date, no research studies have been carried out to evaluate the behavior of the SDCL steel bridge system in high seismic regions. The SDCL concept for seismic regions requires a suitable connection between the girder and pier. The research presented in this paper investigates an integral pier SDCL steel bridge system. The structural behavior and force resistance mechanism of a proposed seismic detail was evaluated through an analytical study. An equation was developed to predict the ultimate connection capacity under seismic loading. This paper presents the results of Phase I of an ongoing, three-phase effort, that will culminate in the development of a set of details and associated design provisions to develop a version of the SDCL steel bridge system suitable for use in high seismic regions.

Enhancement of seismic performance of beam-column joint connections using high performance fiber reinforced cementitious composites

In this paper, six half-scale exterior beam-column joint connections are casted and tested under cyclic loads to investigate and evaluate the possibility of using high performance fiber reinforced cementitious composites (HPFRCC) to remove the necessity of confining (transverse) reinforcements and solve the construction problems in beam-column joints under seismic loads. Fiber reinforced cementitious materials used in this study comprises 2% volume fraction of hybrid fiber, hooked end steel fiber and hybrid macro synthetic fibers. The basic mechanical properties of HPFRCC are determined by uniaxial tension and compression tests. The hysteretic behavior, ductility, stiffness, energy dissipation, damping characteristics and cracking patterns of HPFRCC beam-column joint connections are evaluated and compared with those of normal concrete with and without special seismic requirements in joints. The test results revealed that HPFRCC connections considerably enhanced shear and flexural capacity as well as deformation and damage tolerance behavior at post-cracking stage compared to those of normal concrete at ultimate stages. Moreover, the failure mode of HPFRCC specimens changed from shear mode to flexural mode compared to the failure mode of concretes without required seismic details.

Seismic Performance Limitations and Detailing of Slender Reinforced Concrete Walls

Seismic Performance Limitations and Detailing of Slender Reinforced Concrete Walls

Shaking table tests for the experimental verification of the effectiveness of an automated modal parameter monitoring system for existing bridges in seismic areas

Reinforced concrete bridges represent a majority of the Italian stock and they play a primary role to ensure the efficiency of the transportation network and prompt rescue in the case of an emergency. However, most of them have been designed and built according to outdated codes, or even without any seismic detailing. The significant impact of strong motions on the road network as well as the human life and economy emphasizes the need for effective strategies for post-earthquake emergency management and to support rescue operations. The present paper aims at evaluating, against real data, the effectiveness of automated modal parameter monitoring for vibration-based Structural Health Monitoring (SHM) of existing bridges in earthquake prone areas. This objective has been pursued in the context of shaking table tests on a 1:3 scale single span bridge representative of existing highway bridges built in the 60's in Italy. The dynamic response of the structure before and after the application of asynchronous seismic input has been analyzed for damage detection and performance assessment. Results show that partially hidden damage can be remotely detected, thus validating the interesting applicative perspectives of automated output-only modal identification and modal-based damage detection for fast assessment of existing bridges in the early earthquake aftershock. The robustness of the SHM system to sensor overload due to earthquake shaking has been also assessed, demonstrating the applicability of modal-based SHM in seismic regions even in the absence of a measurement chain specifically designed to resolve the large amplitude vibrations induced by earthquakes. Finally, the possibility of complementing modal-based SHM with drift-based estimates is explored.

Comparative Analysis of Existing RC Columns Jacketed with CFRP or FRCC.

Reinforced concrete (RC) columns typical of existing structures often exhibit premature failures during seismic events (i.e., longitudinal bars buckling and shear interaction mechanisms) due to the poor quality concrete and the absence of proper seismic details in the potential plastic hinge region. The Fiber Reinforced Polymers (FRP) externally bonded reinforcement is known to be a valid technique to improve the shear capacity or the ductility of existing RC columns. However, few experimental tests have proven its effectiveness in the case of columns affected by shear interaction mechanisms. In this work, the behavior of existing RC columns with border line behavior between flexure and shear have been investigated in the case of poor quality concrete and light FRP strengthening with local jacketing and medium quality concrete and strong FRP strengthening with local jacketing, in order to highlight the effect of concrete strength on the effectiveness of the retrofit intervention. As an alternative to FRP jacketing; the effectiveness of the Fiber Reinforced Cementitious Composite (FRCC) jacketing for the seismic strengthening of columns with highly deteriorated concrete cover or columns already damaged by an earthquake is also evaluated. Six full-scale RC columns have been tested under cyclic loading: one was used as a control specimen; four were strengthened in the potential plastic hinge region with carbon FRP (CFRP); and one was fully jacketed with FRCC. The comparison between poor and medium quality concrete columns showed that the CFRP local jacketing is more effective in the case of poor quality concrete. The FRCC jacketing appears to be a sound repair strategy and a suitable alternative to the FRP jacketing in case of poor quality; however, more experimental research is needed for improving this retrofit technique.

Experimental seismic performance of a full-scale unreinforced clay-masonry building with flexible timber diaphragms

This paper presents the results of a unidirectional shake-table test performed on a full-scale, single-storey unreinforced masonry building. The specimen represented a typical detached house of the Groningen region of the Netherlands, consisting of double-wythe clay-brick unreinforced masonry walls, without any specific seismic detailing. The building prototype included large openings and a reentrant corner, causing a discontinuity in one of the perimeter walls. The floor was made of timber beams and planks, resulting in a flexible diaphragm. The roof, characterized by a very steep pitch, consisted of a series of timber trusses connected by wood purlins and boards. The two façades perpendicular to the shaking direction were designed to represent two typical gable geometries. An incremental dynamic test was conducted up to the near-collapse state of the specimen, using input ground motions compatible with induced-seismicity scenarios for the examined region. This paper summarizes the main characteristics of the specimen and the shake-table experimental results, illustrating the dynamic response of the structure, the evolution of the damage mechanisms, and the attainment of significant limit states.

Exploring for stratigraphic traps in the Patchawarra Formation, Cooper Basin: an integrated seismic methodology

The Patchawarra Formation is characterised by Permian aged fluvial sediments. The conventional hydrocarbon play lies within fluvial sandstones, attributed to point bar deposits and splays, that are typically overlain by floodbank deposits of shales, mudstones and coals. The nature of the deposition of these sands has resulted in the discovery of stratigraphic traps across the Western Flank of the Cooper Basin, South Australia. Various seismic techniques are being used to search for and identify these traps. High seismic reflectivity of the coals with the low reflectivity of the relatively thin sands, often below seismic resolution, masks a reservoir response. These factors, combined with complex geometry of these reservoirs, prove a difficult play to image and interpret. Standard seismic interpretation has proven challenging when attempting to map fluvial sands. Active project examples within a 196 km2 3D seismic survey detail an evolving seismic interpretation methodology, which is being used to improve the delineation of potential stratigraphic traps. This involves an integration of seismic processing, package mapping, seismic attributes and imaging techniques. The integrated seismic interpretation methodology has proven to be a successful approach in the discovery of stratigraphic and structural-stratigraphic combination traps in parts of the Cooper Basin and is being used to extend the play northwards into the 3D seismic area discussed.

Role of engineers in seismic design and detailing of reinforced concrete buildings in Australia

Australia is not immune to earthquakes and history proves their future location and magnitude cannot be predicted. To ensure life safety in a somewhat uncertain seismic environment, the appropriate design and detailing of reinforced concrete structures will provide a level of resilience so that in a rarer seismic event, the risk of a total collapse of the structure is ideally avoided. To design structures economically for the significantly higher earthquake loads, most of the loading is carried by the inelastic response of the structure. This is why the correct design and detailing of reinforcement to AS 3600, to provide structures with the ductility to respond inelastically to extreme seismic events, is so important. The new SRIA ‘Guide to Seismic Design and Detailing of Reinforced Concrete Buildings in Australia’, is intended to provide guidance on seismic design principles to graduates, practicing engineers with little seismic experience and senior engineers requiring refreshment on the delicate balance between life safety and the client’s cash flow. As Engineers have a role to communicate seismic risk to the community and reduce seismic risk for the community, this publication provides a valuable resource as it contains lists of questions that should be considered in design.