Pedro Delgado

Numerical Simulations of RC Hollow Piers Under Horizontal Cyclic Loading

This article addresses numerical simulations of experimentally tested RC hollow-section piers prone to shear problems under cyclic loading. Detailed nonlinear modeling was applied with 3D FEM discretization using a damage model for concrete and a cyclic behavior model for steel bars represented by uniaxial elements Analyses were supported by parameter calibration based on experimental pier test data. The results confirmed the adequacy of the modeling strategy for simulating shear effects in these piers.

Modelling of Bridges for Inelastic Analysis

The analytical tools necessary for the implementation of inelastic methods for bridges are presented. The chapter starts with available models for the bridge deck and their role in seismic assessment, addressing not only elastic modelling of the deck but also far less explored issues like the verification of deck deformation demands in cases that inelastic behaviour of the deck is unavoidable. Then the topic of modelling bearings and shear keys is presented, which is of paramount importance in the case of bridges, logically followed by the related issue of seismic isolation and energy dissipation devices; modelling of all commonly used isolation and dissipation devices is discussed and practical guidance is provided. The next section is devoted to inelastic modelling of different types of bridge piers, which are the bridge components wherein seismic energy dissipation takes place in non-isolated structures. All types of inelastic models for members, with emphasis on reinforced concrete columns, are presented in a rather detailed way, including both lumped plasticity and distributed plasticity models. Several examples of application of the previously mentioned models to bridges of varying complexity are provided and critically discussed. The last two sections of the chapter deal with modelling of the foundation of bridges and its interaction with the ground. Simple and more sophisticated models for abutments and (surface and deep) foundation members are provided, followed by models for the surrounding ground, with emphasis on the embankments that often play a crucial role in the seismic response of bridges, in particular short ones. Soil-structure interaction modelling of bridges is presented in both its commonly used forms, i.e. linear, as well as nonlinear soil-foundation-bridge interaction analysis in the time domain. These last sections of the chapter also include a brief overview of the characteristics of seismic ground motion which is used as input for the analysis.

EXPERIMENTAL AND NUMERICAL ANALYSIS ON THE CYCLIC BEHAVIOR OF BRIDGE PIERS WITH AND WITHOUT CFRP RETROFIT

The main objective of this paper is to evaluate the cyclic behavior of RC hollow piers, with and without with CFRP retrofit, by comparison of experimental tests results with structural numerical modeling. The retrofit techniques aim to increase the shear strength and the ductility capacity through the establishment of principles and strategies applied in an experimental cyclic campaign of RC hollow piers, carried out in the Laboratory for Earthquake and Structural Engineering (LESE) of the Faculty of Engineering of University of Porto (FEUP). The evaluation and calibration of the efficiency of several retrofit solutions is also performed. The numerical simulations are carried out using two different methodologies: (i) fiber model and (ii) damage model. The fiber models based in a finite element discretiztion with non-linear behavior distributed along the elements length and cross-sectional area, while the damage model is supported on refined finite element (FE) meshes, with high complexity and detail levels in the constitutive laws defined for both concrete and steel. The concrete is simulated with a continuum damage model where several applications for bridges with hollow section piers can be found at Faria et al. [1]. Results of the experimental campaign allow to discuss and conclude about the efficiency of each numerical method, namely regarding the shear strength and the ductility capacity assessment.

Non Linear Shear Effects on the Cyclic Behaviour of RC Hollow Piers

Reinforced concrete (RC) hollow section piers have been the subject of several studies in the recent past, from which one important drawn conclusion is the significant influence of shear effects on these piers behaviour, particularly under cyclic loading. In that framework, tests were carried out at Laboratory of Earthquake and Structural Engineering (LESE) from Faculty of Engineering of University of Porto (FEUP) on several reduced scale (1:4) RC hollow section bridge piers under lateral cyclic loading with constant axial force reported by Delgado (Bull Earthquake Eng 7:377−389, 2009). This work aims at presenting the numerical simulations performed for some of the referred piers in order to better understand phenomena associated with its cyclic behaviour, as observed in the experimental campaign. The numerical strategy was based on refined 3D Finite Element Mesh (FEM) discretization using a two-scalar variable damage model for the concrete constitutive law and a suitable cyclic behaviour law for steel bars represented by uniaxial elements. As is well known, the shear effects are complex phenomena involving the global behaviour of the structural elements and where the non linear effects have a crucial role. In this chapter a detailed modelling was used allowing for realistic simulations of the non linear behaviour, which was found particularly suitable when significant shear effects are involved. The bond between the bars and the embedding concrete, by incorporating a bond stress—slip behaviour law in the numerical calculations is considered, an effect particularly important when thin plain steel bars are considered, as is the case of the tested piers. The adopted formulation is similar to the well known Eligehausen proposals although with slightly modified cyclic behaviour parameters.

Strengthening of RC Bridges

During past seismic events several cases of concrete bridges with poor structural behaviour and severe damage were reported. In this chapter, common damage patterns in RC bridges are illustrated, with reference to several previous studies about the seismic performance of bridge components. The focus of the chapter is on pier behaviour, wherein damage is usually more significant and quite often there is a need to retrofit these elements. In this context, the main objective of this chapter is to present the most common retrofitting strategies for RC bridges and the resulting benefits to their structural behaviour. Several types of piers are considered, where the cross section ranges from solid to hollow and from circular to rectangular. One of the most common retrofit measures for RC bridge piers is the full or partial jacket, which can be made in FRP, steel or RC. Experimental and numerical tests were carried out to assess the benefits to bridge pier behaviour, resulting from shear strengthening of piers with hollow cross section. Moreover, analytical studies are presented on the performance of bridges retrofitted using different techniques, aiming at strengthening and/or confinement, and a method for assessing the seismic fragility of retrofitted bridges is described, along with an application to a bridge with circular piers.

COST OF REPAIR AND RETROFIT OF SEISMIC DAMAGE OF RC HOLLOW-PIERS

Reinforced concrete hollow piers are well known for the shear effects they so often reveal to be subjected to. This aspect is particularly true in the case of hollow piers where the failure modes usually relate to shear behavior. Very few studies have devoted their attention to the economic consequences of repairing and retrofitting the physical damages existing in RC hollow piers subjected to the seismic action. This information is deemed crucial when cost-benefit analysis is concerned for the definition of measures for repair and retrofit of seismic damage. Therefore, the present work intends to discuss adequate strengthening strategies and their costs, associated with each seismic physical limit state of damage. An extensive review of numerous cyclic experimental works on RC hollow piers conducted at the University of Porto will be performed, and in liaise with specialized construction companies, the repair costs will be estimated. 703 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 703-719

NUMERICAL SEISMIC SAFETY ASSESSMENT OF RC BRIDGES WITH HOLLOW PIERS

The seismic damages of reinforced concrete bridges in recent events show that many of them have an inadequate behavior and safety. Therefore, is important to accurately define bridge safety assessment and hence evaluate the accuracy of the analytical methodologies for seismic response of bridges. The main objective of this paper is to present several options for structural simulation with different complexities in order to assess the seismic response of bridges and then use the results for the safety assessment with probabilistic approaches. The numerical simulations are carried out using three different methodologies: (i) plastic hinge model, (ii) fiber model and (iii) damage model. Seismic response of bridges is based on a simplified plane model, with easy practical application and involving reduced calculation efforts while maintaining adequate accuracy. The evaluation of seismic vulnerability is carried out through the failure probability quantification involving a non-linear transformation of the seismic action in its structural effects. The applicability of the proposed methodologies is then illustrated in the seismic analysis of two reinforced concrete bridges, involving a series of experimental tests and numerical analysis, providing an excellent set of results for comparison and global calibration.

EXPERIMENTAL CYCLIC TESTS OF HOLLOW PIERS WITH DIFFERENT RETROFIT STRATEGIES

Abstract. An experimental cyclic campaign of RC hollow piers has being carried out in the Laboratory for Earthquake and Structural Engineering (LESE) of the Faculty of Engineering of University of Porto (FEUP), aiming to establish, among other purposes, a strategy to retrofit RC hollow piers subjected to horizontal cyclic actions with axial load. The retrofit techniques intend to increase the shear strength and the ductility capacity through the application of CFRP sheets. The main objective of this paper is to evaluate and calibrate the efficiency of several retrofit solutions. The design criteria for the piers retrofit solutions and the different strategies for the practical application are presented, namely, the CFRP sheets for shear retrofit and CFRP base strip, with or without steel bars applied inside the hollow box, for ductility improvement, being the different types of retrofit grouped out in order to understand the main benefits of each one. Results of the experimental campaign allow to discuss and conclude about the efficiency of each retrofit solution, explicitly regarding the improvement of the shear strength and the ductility capacity.

Case Studies and Comparative Evaluation of Methods

The methods presented in chapter 3 are applied here to specific case-studies, involving bridges with different length and configuration. The chapter starts with a critical discussion of the basic parameters that influence the applicability of pushover methods. Then, a number of case-studies are presented in a rather uniform and detailed way; they were selected among those available with a view to including at least one application of each category of methods described in the previous chapter and (wherever feasible) to applying two or more ‘simplified’ methods to the same bridge structure. In addition to a number of pushover analyses, all case-studies include also response-history analysis of the inelastic response of the bridge, which serves as a reference for evaluating the results of the various approximate (static) procedures. In the case studies, in addition to the four pushover methods described in detail in Chapter 3, some other variants of the key approaches are also used and comparatively evaluated, so that at the end a more global picture of practically all analysis and assessment techniques available for bridges is provided. To allow for an even broader view on the issues involved and put the purely analytical methods into the proper perspective, the final section of chapter 4 presents an experimental evaluation of analytical methods, i.e. results from analytical methods (response-history, as well as pushover) are compared with those from the shaking table testing (using three shaking tables) of a 1:4 scale bridge model.