2.2 Concrete Structures I
Hysteresis Behaviour of Reinforced Concrete Non-Ductile Beam-Column Joints
Piyali Sengupta & Bing Li
ABSTRACT: This paper demonstrates an analytical approach for predicting the hysteresis behaviour of nonseismically detailed reinforced concrete beam-column joints. Considering the versatility and mathematical tractability of Bouc-Wen-Baber-Noori model for single-degree-of-freedom system, this model has been adopted with suitable modification for the research. The model, in its analytical form of a set of differential equations, can capture the true characteristics of non-ductile reinforced concrete beam-column joints, like stiffness and strength degradation, pinching, softening and hardening. Livermore Solver for Ordinary Differential Equations of double precision version has been used for solving the differential equations, involved in the model. As different parameters included in the differential equations take care of different characteristics, Genetic Algorithm has been selected as a parameter estimation tool to generate parameter magnitudes with reasonable accuracy. The analytical responses have been compared with the experimental results of six internal and six external non-ductile reinforced concrete beam-column joints from literature. Good correlation between the analytical and experimental results proves the effectiveness of the model and accuracy of the solver and algorithm.
Shake Table Tests of Non-Ductile As-Built and Repaired RC Frames
P.Quintana Gallo, U. Akgüzel, S. Pampanin & A.J. Carr
ABSTRACT: In order to provide information related to seismic vulnerability of non-ductile reinforced concrete (RC) frame buildings, and as a complementary investigation on innovative feasible retrofit solutions developed in the past six years at the University of Canterbury on pre-19170 reinforced concrete buildings, a frame building representative of older construction practice was tested on the shake table. The specimen, 1/2.5 scale, consists of two 3-storey 2-bay asymmetric frames in parallel, one interior and one exterior, jointed together by transverse beams and floor slabs. The as-built (benchmark) specimen was first tested under increasing ground motion amplitudes using records from Loma Prieta Earthquake (California, 1989) and suffered significant damage at the upper floor, most of it due to lap splices failure. As a consequence, in a second stage, the specimen was repaired and modified by removing the concrete in the lap splice region, welding the column longitudinal bars, replacing the removed concrete with structural mortar, and injecting cracks with epoxy resin. The modified as-built specimen was then tested using data recorded during Darfield (New Zealand, 2010) and Maule (Chile, 2010) Earthquakes, with whom the specimen showed remarkably different responses attributed to the main variation in frequency content and duration. In this contribution, the seismic performance of the three series of experiments are presented and compared.
Seismic Behaviour of RC Columns with Light Transverse Reinforcement under Different Loading Directions
Bing Li & Thanh Phuong Pham
ABSTRACT: This paper presents an experimental investigation carried out on reinforced concrete (RC) columns with light transverse reinforcements. Seven half-scale RC columns are tested to the point of axial failure to study the seismic behaviour of such columns. Quasi-static cyclic loading simulating earthquake actions are applied along with constant axial forces. The study emphasizes on how varying angles of seismic loads influence the seismic performance of the columns. The overall performance of each specimen is examined in terms of the cracking patterns, hysteretic response, shear strength and drift ratio at axial failure. The direction of seismic loads is found, as a major finding, to have significant effects on the drift capacities and failure modes for both rectangular columns and square columns. Besides, shear strength of columns under seismic load with different angles can be analytically predicted.
Application of Post-Installed Anchors for Seismic Retrofit of RC Beam-Column Joints: Design Method
G. Genesio, R. Eligehausen & S. Pampanin
ABSTRACT: Many reinforced concrete (RC) structures, built in seismic-prone countries before the introduction of the modern seismic oriented codes and usually designed for gravity loads only, necessitate an upgrade in terms of strength and ductility against lateral loading. In this paper the possibility of using post-installed anchors for seismic retrofit solutions is investigated. Post-installed anchors are usually fast and easy to install and they represent a valuable low-invasive solution to transfer high loads with quite low costs. The retrofit of RC beam-column connections with a diagonal haunch element fastened to the existing structural element using post-installed anchors is proposed. The design method based on experimental and analytical investigations is presented. Particular focus is given to the requirements in terms of load displacement characteristics, i.e. stiffness on the post-installed anchors.
Effects of Bond Deterioration due to Corrosion in Reinforced Concrete
A. Palermo & A. Scott
ABSTRACT: Reinforced concrete structures exposed to aggressive environments throughout their design life often sustain high levels of deterioration due to corrosion of reinforcement. This causes large losses in cross-section and diminished bond performance resulting in reduced performance under seismic and everyday loading. This paper assesses the monotonic and cyclic bond performance of corroded reinforcing through a series of 24 tests that focus on reductions in bar cross-section between 15-25%. The effects of high levels of corrosion were substantial with over 50% reduction in bond rupture stress resulting from only 15% reduction in cross-sectional area due to corrosion. More importantly, when subjected to cyclic loading, the rate of bond degradation was much higher than would be expected if the uncorroded result was simply scaled by the reduced rupture stress.
The Effect of Reinforcement Strength on the Overstrength Factor for Reinforced Concrete Beams
N.J. Brooke & J.M. Ingham
ABSTRACT: The design of earthquake resistant structures in New Zealand is based around the philosophy known as capacity design. In order for this philosophy to be successfully applied, it is essential that the flexural overstrength factor is appropriately defined. Overstrength factors for reinforced concrete structures are defined in the New Zealand Concrete Structures Standard, NZS 3101:2006, which currently prescribes the flexural overstrength factor for beams as 1.25 if the beam contains Grade 300E longitudinal reinforcement and as 1.35 if the beam contains Grade 500E longitudinal reinforcement. However, review of existing literature and consideration of structural behaviour does not support the use of different overstrength factors for different types of reinforcement. Analysis of a database of approximately one hundred beam-column joint tests indicates that the same overstrength factor should be used for reinforced concrete beams irrespective of whether they contain Grade 300E or Grade 500E longitudinal reinforcement.