Vassilis K. Papanikolaou

EVALUATION OF CONVENTIONAL AND ADAPTIVE PUSHOVER ANALYSIS I: METHODOLOGY

In this paper, a methodology is suggested and tested for evaluating the relative performance of conventional and adaptive pushover methods for seismic response assessment. The basis of the evaluation procedure is a quantitative measure for the difference in response between these methods and inelastic dynamic analysis which is deemed to be the most accurate. Various structural levels of evaluation and different incremental representations for dynamic analysis are also suggested. This method is applied on a set of eight different reinforced concrete structural systems subjected to various strong motion records. Sample results are presented and discussed while the full results are presented alongside conclusions and recommendations, in a companion paper.

EVALUATION OF CONVENTIONAL AND ADAPTIVE PUSHOVER ANALYSIS II: COMPARATIVE RESULTS

In this paper, the methodology for evaluation of conventional and adaptive pushover analysis presented in a companion paper is applied to a set of eight different reinforced concrete buildings, covering various levels of irregularity in plan and elevation, structural ductility and directional effects. An extensive series of pushover analysis results, monitored on various levels is presented and compared to inelastic dynamic analysis under various strong motion records, using a new quantitative measure. It is concluded that advanced (adaptive) pushover analysis often gives results superior to those from conventional pushover. However, the consistency of the improvement is unreliable. It is also emphasised that global response parameter comparisons often give an incomplete and sometimes even misleading impression of the performance.

Nonlinear dynamic analysis of masonry buildings and definition of seismic damage states

A large part of the building stock in seismic-prone areas worldwide are masonry structures that have been designed without seismic design considerations. Proper seismic assessment of such structures is quite a challenge, particularly so if their response well into the inelastic range, up to local or global failure, has to be predicted, as typically required in fragility analysis. A critical issue in this respect is the absence of rigid diaphragm action (due to the presence of relatively flexible floors), which renders particularly cumbersome the application of popular and convenient nonlinear analysis methods like the static pushover analysis. These issues are addressed in this paper that focusses on a masonry building representative of Southern European practice, which is analysed in both its pristine condition and after applying retrofitting schemes typical of those implemented in pre-earthquake strengthening programmes. Nonlinear behaviour is evaluated using dynamic response-history analysis, which is found to be more effective and even easier to apply in this type of building wherein critical modes are of a local nature, due to the absence of diaphragm action. Fragility curves are then derived for both the initial and the strengthened building, exploring alternative definitions of seismic damage states, including some proposals originating from recent international research programmes.

Elastic analysis and application tables of rectangular plates with unilateral contact support conditions

Abstract In the present study, a numerical methodology for the elastic analysis of single plates is presented, which takes into account any unilateral support conditions (uplift potential) that can occur in one or more supporting boundaries. The plates are discretized with a fine mesh of finite elements and the unilateral support conditions are simulated through proper link elements, while the determination of the uplifted regions of the plates is part of the problems solution. A parametric study is then carried out for rectangular edge-supported plates for various combinations of support conditions and aspect ratios. From the processing of the results of this analysis, proper application tables for the calculation of stress state of the plates were created, in a form similar to the well-known tables compiled by Czerny.

Vulnerability assessment and feasibility analysis of seismic strengthening of school buildings

Abstract The majority of structures in seismic-prone areas worldwide are structures that have been designed either without seismic design considerations, or using codes of practice that are seriously inadequate in the light of current seismic design principles. In Cyprus, after a series of earthquakes that occurred between 1995 and 1999, it was decided to carry out an unprecedented internationally seismic retrofitting of all school buildings, taking into account the sensitivity of the society towards these structures. In this paper representative school buildings are analysed in both their pristine condition and after applying retrofitting schemes typical of those implemented in the aforementioned large-scale strengthening programme. Non-linear analysis is conducted on calibrated analytical models of the selected buildings and fragility curves are derived for typical reinforced concrete and unreinforced masonry structures. These curves are then used to carry out a feasibility study, including both benefit-cost and life-cycle analysis, and evaluate the effectiveness of the strengthening programme.

CONCRETE-TO-CONCRETE INTERFACES UNDER CYCLIC LOADING: FINITE ELEMENT ANALYSIS TOWARDS EXPERIMENTAL VERIFICATION

The objective of this paper is to describe a novel experimental setup for testing the concrete-to-concrete interface behavior under cyclic loading. Within the suggested configuration, various investigation parameters can be facilitated, such as the variation of concrete properties, interface roughness and number of transverse dowels. The specimen consists of three distinct concrete blocks in contact, as to create symmetric double interfaces. The middle concrete block has different concrete compressive strength, which suggests interfaces cast in different times. For the specimen preparation, elaborate computer-aided manufacturing (CAM) methods such as 3D design, laser-cutting and CNC-milling have been utilized. Moreover, an ad-hoc numerical analysis is performed, in the form of a blind-test procedure against its forthcoming experimental counterpart. The analysis is based on a three-dimensional nonlinear finite element model, accurately describing the physical specimen properties and loading setup. The analytical results are presented in a form of interface shear stress vs. slip, stress variation contours along the interface area and dowel tensile stress. A comparison with Code-based recommendations is performed and various interesting points are highlighted.

Nonlinear Static and Dynamic Behavior of a 16-Story Torsionally Sensitive Building Designed According to Eurocodes

A 16-story building under construction in Bucharest has been designed according to the provisions of EC2 and EC8, using elastic spectral modal analysis. Considering that the building is torsionally sensitive in the nonlinear range, it was further checked and verified using nonlinear dynamic and static procedures, using a detailed space-frame model. Specifically, time-history analysis for seven different excitations, as well as respective inelastic static analysis taking into account torsional effects were performed. The results are examined regarding structural (global) and member (local) response and various issues concerning the adequacy of the original elastic design and the applicability of advanced analysis methods are discussed.

EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF AN UNCONVENTIONAL, ROCKING TYPE RESPONSE MECHANISM FOR EARTHQUAKE-RESISTANT BRIDGES

Abstract. In the present study a new technique is investigated, which takes advantage of the rocking principle for the treatment of the two ambivalent demands in bridge designing, i.e. due to seismic and serviceability actions. The idea is based on the formation of cracks only in two positions on each bridge pier, which are the pier cross-sections in contact with the deck and the pile cap respectively, excluding the possibility of cracking in the mid-length of the piers. The possibility of flexural crack formation in one of these cross-sections was examined experimentally in order to reach the above objective. This was achieved through partial suppression of the longitudinal reinforcement bond with the surrounding concrete. In order to confirm the feasibility of the above objective and to verify the influence of the bond suppression on all three response indexes, namely strength, stiffness and ductility, eight experimental specimens in the form of cantilevers, representing ductile bridge piers, were prepared. The varying parameter was the shear span ratio. Useful results were observed regarding the three response indexes and interesting conclusions were obtained.