Murat Saatcioglu

RESPONSE OF REINFORCED CONCRETE COLUMNS TO SIMULATED SEISMIC LOADING

Response of reinforced concrete columns to seismic loading was investigated experimentally. Full-scale columns were tested under slowly applied lateral reversals. Both unidirectional and bidirectional loadings were included. Columns with and without axial loads, including variable axial tension and compression, were tested. The test parameters included: axial load, shear/confinement reinforcement, and deformation path. Test results indicate that axial loads have a significant influence on hysteretic response of columns. Column capacity changes with the concurrent level of axial load, axial compression reduces column response, and bidirectional load cycles can produce severe strength and stiffness degradation.

Inelastic analysis of reinforced concrete columns

Abstract A computer software was developed for inelastic analysis of reinforced concrete columns under combined axial compression and monotonically increasing lateral loads. The software incorporates effects of concrete confinement, steel strain hardening, reinforcement buckling, and secondary deformations due to P – Δ effect. Hinging of column critical region and progression of hinging along column height are considered. Inelastic deformation components due to flexure and anchorage slip are included. The input consists of column geometry, material properties, and loading. The results are presented in a graphical form in terms of moment–curvature, force–displacement, and moment–anchorage slip relationships. Axial force–moment interaction diagram is also plotted as part of the output. The program was verified extensively against available experimental data.

Rectangular Stress Block for High-Strength Concrete

The use of high-strength concrete (HSC), with strengths reaching 130 MPa, has increased in recent years due to its superior performance. Structures are designed and built using HSC, especially in columns of multistory structures. The rectangular stress block specified in the ACI 318-02 Building Code for design of reinforced concrete elements was developed, however, on the basis of normal-strength concrete column tests. The applicability of the ACI rectangular stress block to higher-strength concretes becomes questionable, especially for members under high levels of axial compression. A new rectangular stress block is introduced in this paper for a wide range of concrete strengths between 20 and 130 MPa. The proposed stress block is verified against available test data. Column strengths computed using the stress block show good agreement with those recorded experimentally.

Performance of Structures in Indonesia during the December 2004 Great Sumatra Earthquake and Indian Ocean Tsunami

A reconnaissance was conducted in Indonesia to investigate the effects of the 26 December 2004 earthquake and tsunami on buildings, bridges, and other physical infrastructure. The infrastructure in the coastal regions of Banda Aceh was completely devastated by both tsunami wave pressures and seismic ground excitations. The damaging effects of the tsunami were most pronounced in unreinforced masonry walls, nonengineered reinforced concrete buildings, and low-rise timber-framed buildings. Engineered structures survived the tsunami pressure, but many suffered extensive damage due to seismic forces. The majority of the seismic damage was attributed to poor design and detailing of nonductile buildings. Specific observations made during the reconnaissance indicate the engineering significance of the disaster.

Risk-Based Seismic Evaluation of Reinforced Concrete Buildings

Seismic resiliency of new buildings has improved over the years due to improved seismic codes and design practices. However, vulnerability of seismically deficient older buildings, designed and built on the basis of older codes of practices, poses a significant threat to life safety and survivability of buildings. It is economically not feasible to retrofit the entire inventory of seismically deficient buildings. Therefore, there is need for a comprehensive plan to identify critical buildings and prioritize their retrofit and upgrading requirements. A risk-based evaluation technique is proposed in this paper to quantify seismic assessment and develop a ranking scheme for reinforced concrete buildings. The seismic hazard, building vulnerability and consequence of failure are handled in hierarchical structures. Some of the input risk parameters, expressed as qualitative and quantitative quantifiers, are transformed into commensurable values. A knowledge-based fuzzy rule base modelling is developed and verified through the use of 1994 Northridge Earthquake data on seismic damage of reinforced concrete buildings.

DISPLACEMENT-BASED DESIGN OF REINFORCED CONCRETE COLUMNS FOR CONFINEMENT

This paper describes a displacement-based design procedure developed for confinement of earthquake-resistant concrete columns. The procedure is based on experimentally observed and analytically computed relationships among the parameters of confinement. The amount, grade, spacing, and arrangement of transverse reinforcement; concrete strength and cover thickness; and level of axial compression and drift ratio were considered as parameters of confinement. Static inelastic analyses were conducted to generate a large volume of data, with consideration given to concrete confinement, reinforcement strain hardening and buckling, anchorage slip, axial compression, and secondary deformations due to P-delta effect. Both normal-strength and high-strength concrete columns with circular and square cross sections were included. Improved design expressions were developed for column confinement utilizing both the current design criterion, which is based on column axial deformability, and the recommended design criterion, which is based on lateral deformability as expressed by column drift ratio.

Seismic Vulnerability Assessment of Reinforced Concrete Buildings Using Hierarchical Fuzzy Rule Base Modeling

A reliable building vulnerability assessment is required for developing a risk-based assessment and retrofit prioritization. Tesfamariam and Saatcioglu (2008) proposed a simple building vulnerability module where the building performance modifiers are in congruence with FEMA 154. This paper is an extension of the building vulnerability assessment that include detailed performance modifier in congruence with FEMA 310 that is represented in a heuristic based hierarchical structure. Some of the input parameters are obtained through a walk down survey and are subject to vagueness uncertainty that is modelled through fuzzy set theory. A knowledge base fuzzy rule base modeling is developed and illustrated for reinforced concrete buildings damaged in the 1 May 2003 Bingöl, Turkey earthquake.

Evolution of seismic design provisions in the National building code of Canada

The purpose of this paper is to provide a summary of the evolution of seismic design in Canada. This paper presents the significant changes to the approach taken in determining seismic hazards and seismic hazard maps, and describes the evolution of the seismic design provisions of the National building code of Canada. The introduction of important parameters in determining the seismic base shear such as the period of vibration of the structure, the influence of type of soil, and the concepts of ductility and energy dissipation capacity of elements and structures are presented. The levels of seismic design base shears, determined from different versions of the National Building Code of Canada, are compared for reinforced concrete frame and wall structures to illustrate the changes.

Confinement of Reinforced Concrete Columns With Welded Wire Fabric

The behavior of reinforced concrete columns confined with welded-wire fabric was investigated. Thirty-four small-scale column specimens with different reinforcement arrangements, inlcuding four corner bars as longitudinal reinforcement and various combinations of welded-wire fabric and tie steel as lateral reinforcement, were tested under conentric loading. The results indicate that welded-wire fabric can be effective in confining the core concrete, resulting in significant improvements in strength and ductility of columns. This improvement, which is achieved with a relatively small percentage of steel, is equivalent to that achieved with closely spaced tie and longidutinal reinforcement with a considerable larger steel percentage. Although some practical problems remain, welded-wire fabric can potentially be used in earthquake-resistant structures as confinement reinforcement.

Seismic Performance of Masonry Infill Walls Retrofitted With CFRP Sheets

Synopsis: A significant portion of existing building stock that was constructed prior to the enactment of modern seismic design provisions consists of gravity-load-designed reinforced concrete frames, infilled with unreinforced masonry walls. These structures are susceptible to extensive seismic damage when subjected to strong earthquakes and require retrofitting in order to comply with the provisions of current building codes. Experimental investigation of gravity-load-designed reinforced concrete frames, infilled with concrete block masonry, has been conducted to develop a seismic retrofit strategy that involves the use carbon fiber reinforced polymer (CFRP) sheets. Two half-scale concrete frames, infilled with masonry walls were tested with and without seismic retrofitting. The retrofit technique consisted of CFRP sheets, surface bonded on the masonry wall, while also anchored to the surrounding concrete frame by means of specially developed CFRP anchors. The frame-wall assemblies were tested under constant gravity loads and incrementally increasing lateral deformation reversals. The results indicate that infilled frames without a seismic retrofit develop extensive cracking in the walls and frame elements. The elastic rigidity reduces considerably resulting in softer structure. The failure may occur in non-ductile frame elements, especially in columns. Retrofitting with CFRP sheets controls cracking and increases lateral bracing, improving the elastic capacity of overall structural system. The retrofitted specimen tested in the current investigation showed approximately 300% increase in lateral force resistance, promoting elastic response to earthquake loads as a seismic retrofit strategy. Experimental observations and results are presented in the paper.