The effect of preloading on the strength of jacketed R/C columns

The influence of core preloading on the strength of jacketed reinforced concrete (R/C) columns is analytically investigated. A recently proposed method for arbitrary composite section analysis in biaxial bending and axial load is extended to include preloading actions. A parametric evaluation of the preloading effect using quantitative indices is performed, considering the variability of several parameters such as section geometry, amount of reinforcement, and various axial and moment preloading levels. Results are presented in the form of 3D failure surfaces and moment-curvature curves. Specific cases where the preloading effect is more pronounced are finally highlighted

A FEM-based model to study the behavior of SRG-strengthened R/C beams

In this paper, a new time‐effective modeling approach is proposed for predicting the response of shear‐deficientreinforced concrete (R/C) beams strengthened with steel‐reinforced grout (SRG) jackets. Solid finite elementsare utilized for concrete using a fracture‐plasticity constitutive law, while both high‐strength steel cords andconventional reinforcement are modeled using embedded truss elements with multilinear stress–strain laws.The efficiency of the proposed method is assessed by comparing numerical against experimental data of nineshear‐deficient beams strengthened with various SRG jacketing configurations. The comparison demonstratedclose correlation both in terms of failure mode and force–displacement curves. The numerical analysis predicted the observed crack pattern and failure modes accurately, whereas deviation in terms of load and deflection was, on average, less than 1% and 10%, respectivel

Flexural behaviour of reinforced concrete jacketed columns under reversed cyclic loading

The objective of the present study is the development of an analytical model for predicting the response under reversed cyclic loading of structural members with ‘old-type’ detailing, strengthened with reinforced concrete (RC) jacketing. The analytical model introduces one additional degree of freedom between the existing member (core of the retrofitted member) and its outer RC shell, thus allowing slip to take place at the interface between the existing member and the jacket. Shear resistance mechanisms, such as aggregate interlock, friction, and dowel action, are mobilized to resist slip. Existing constitutive models are further improved to describe the mechanisms that resist sliding under cyclic shear reversals and implemented for the first time in an analytical model for deriving the response of RC jacketed members. A calculation algorithm is developed to estimate the flexural response under cyclic loading taking into account slip at the interfaces. The sensitivity of the proposed analytical model to the shear transfer mechanisms degradation rules, as well as to the crack spacing estimation, was evaluated. The validity of the proposed analytical model is assessed against experimental results

Practical nonlinear analysis of unreinforced concrete tunnel linings

A comprehensive methodology for modelling, analyzing and assessing the structural response of unreinforced concrete tunnel linings is presented. Various modelling techniques are described, considering the plane finite element representation of the lining geometry, material constitutive laws, and boundary and interface conditions. Furthermore, all relevant external loading cases are studied, including gravity, environmental, fire, blast, and seismic loading. Potential pitfalls in the modelling and analysis procedures are identified and properly dealt with. The suggested methodology is finally applied to actual tunnel linings and the interpretation of the analysis results leads to important conclusions regarding the applicability of different analysis methods and the performance of unreinforced concrete linings

Limits of Applicability of Conventional and Advance Pushover Analysis for Seismic Response Assessment

In this report, the applicability of conventional and advanced inelastic static (pushover) analysis for seismic response assessment is investigated. A methodology is first suggested for evaluating the performance of pushover methods, based on a quantitative measure for the difference in response between pushover and inelastic dynamic analysis which is deemed to be the most accurate, but still expensive numerical method available. This methodology is applied on a set of eight different structural systems, covering various levels of irregularity in plan and elevation, structural ductility and directional effects. An extensive series of pushover analysis results, monitored on various structural levels is presented and compared to inelastic dynamic analysis under various strong motion records. General conclusions on the applicability of inelastic static analysis for seismic response assessment are finally discussed.National Science Foundation EEC-9701785published or submitted for publicatio

Zeus NL - A System for Inelastic Analysis of Structures

This the executible file to download the Zeus NL software, Version 1.8.7.National Science Foundation EEC-971078

A Low-Cost Instrumentation System for Seismic Hazard Assessment in Urban Areas

The development and application of a low-cost instrumentation system for seismic hazard assessment in urban areas are described in the present study. The system comprises a number of autonomous triaxial accelerographs, designed and manufactured in house and together with dedicated software for device configuration, data collection and further postprocessing. The main objective is to produce a detailed view of strong motion variability in urban areas, for at least light intensity strong motion events. The overall cost of the developed devices is at least ten times lower than the respective commercial units, hence their deployment as an ultra-dense network over the area of interest can be significantly cost-effective. This approach is considered an efficient complement to traditional microzonation procedures, which are typically based on relatively few actual recordings and the application of theoretical methodologies to assess the strong motion distribution. The manufactured devices adopt micro-electro-mechanical (MEMS) digital sensor technology for recording acceleration, whereas the accompanying software suite provides various configuration options, quick browsing, analyzing and exporting of the recorded events, as well as GIS type functionality for seamlessly producing explicit seismic hazard maps of the considered area. The evaluation of system performance was based on shaking table and real field comparisons against high accuracy commercial accelerographs. The study concludes with a real application of the proposed system in the form of an ultra-dense network installed at the city of Lefkada, an earthquake prone urban area in Greece, and the following compilation of explicit shakemaps

Experimental and numerical investigation of the uniaxial compression behavior of SRG-Jacketed R/C columns

This paper presents an experimental and numerical investigation of Reinforced Concrete (R/C) short columns strengthened with Steel Reinforced Grout (SRG) jackets. Nine specimens were constructed and tested under concentric monotonic uniaxial compression, measuring compressive force, axial and lateral displacements. Parameters of investigation were the influence of internal steel reinforcement (i.e. no reinforcement, sparse or dense stirrups) and the number of the externally applied SRG jackets (i.e. one or two layers). Subsequently, a three-dimensional finite element methodology was developed, aiming to predict the response of those specimens. Experimental results show that the strength and deformation capacity of the specimens was significantly enhanced with the addition of the SRG jackets, since the strengthening schemes provided sufficient passive confinement. The comparison between experimental and numerical results, in terms of failure mode, axial and lateral stress–strain curves, demonstrated satisfying correlation, proving the efficiency of the proposed numerical model