Measuring Dynamic Impaction Aged Timber Bridges: Some Experimental Options

There are thousands of aged timber beam bridges on local roads in New South Wales (NSW) and because of deterioration their safety levels are unknown. To identify a bridge safety level requires a structural performance measurement, preferably with a Structural Health Monitoring (SHM) system, so that any significant temporal change can be quickly identified. There is a need, however, to identify sensors and systems that can be used to monitor the dynamic impact of loads moving at highway speeds that are of adequate performance and of a cost that is a small fraction of the structures' value. Three measurement systems are considered: a high speed camera system to enable the establishment of base-line performance; a laser sensor system to enable accurate validation of other measurement systems on in-service structures; and a system comprising accelerometers to provide a relative motion record of components compared to the motion of a main girder

Upgrading of Reinforced Concrete Joints with Carbon Fibre Sheets

This paper presents the results of an experimental study performed in order to evaluate the ability of CFRP sheets in upgrading an exterior RC joint by preventing the plastic hinge formation at the face of the column. In this study, three 1/2.2 scaled-down RC exterior joints of a typical Ordinary Moment Resisting Frame (OMRF) were tested under monotonic load. One specimen was used as a control while the other two were strengthened with CFRP sheets of different lengths. All specimens were loaded monotonically to failure under a displacement-controlled regime. The results show that (when carefully designed), carbon fibre sheets can effectively relocate the plastic hinge away from the face of the column. Non-linear numerical analysis using ANSYS provided an insight to the expected failure mechanism and to this phenomenon. In this paper, the results of the experiments and the numerical analyses are presented and discussed

Estimation of the Ductility of Web-Bonded FRP Beams for Assessment of Strengthened RC Exterior Joints

Beam-column joints in Reinforced Concrete (RC) moment resisting frame (MRF) subjected to lateral loads can be critical regions. They must therefore be designed adequately in order 10 dissipate large amounts of energy without a significant loss of strength and ductility. When the joint are inadequately designed or damaged under unanticipated loads, web-bonded FRP is one of the possible strengthening methods that can be used. In this paper, a computer model is presented in order to estimate the ductility of strengthened beams and a range of possible design charts is produced to select the type and amount of FRP required for upgrading exterior beam-column joints. Finally, displacement ductility of a subassembly is assessed using these design charts and the result is compared with experiment. The comparison proves the model is acceptable

Nonlinear Finite Element Modelling of FRP Strengthened RC Beam-column Joints

A research study was conducted at the University of Queensland in order to evaluate the ability of CFRP web-bonded systems in strengthening an exterior beam-column joint subjected to monotonic loads. As part of this study, one 1/2.2 scaled plain and two CFRP retrofitted joints subjected to monotonic loads were tested and analysed using the nonlinear finite-element program ANSYS. A modified version of the Hognestad's model was used to model the concrete compressive strength and the ANSYS model was employed in order to account for tension stiffening in concrete after cracking. In order to model the stress-strain properties of main steel bars a multilinear isotropic hardening model was considered. For FRPs however an anisotropic model was used. Perfect bond between materials was assumed as nodes were shared between adjacent elements irrespective of their type. Good agreement between the numerical predictions and the experimental observation of the failure mechanisms for all specimens was observed. This proved that the numerical analysis could be used as a practical tool for the analysis of web-bonded FRP strengthened beam-column joints

A Short State-of-the-Art Review on Construction and Settlement of Soft Clay Soil Reinforced with Stone Column

The primary application of various geotechnical construction techniques is for ground improvement. Many soil improvement methods have been developed due to the ongoing increase in urban and industrial growth and the need for greater access to lands. Stone columns are one of the best available techniques for soft clay soil improvement. In this method, subsurface soils which are weak and unstable are replaced with compacted dense aggregate columns that often entirely penetrate into the weak layers. This paper aims to present a short state-of-the art on the stone column ground improvement technique based on existing literature and standards. Due to high permeability of the material component used in the stone columns, not only the load carrying capacity of the soil is raised, but also the soil settlement is reduced considerably and the post construction settlement is minimized. To achieve this goal, several significant characteristics of stone column in terms of design parameters are considered. One example of the behavior assessment of reinforced soil using stone column is included. A new one-dimensional analysis has been studied in addition to a simplified nonlinear finite element method. The results indicate that the new method is reliable. It is also indicated that the settlement of the soil without stone columns is significantly higher than the similar soil reinforced with stone column

Seismic Resilience of Retrofitted Reinforced Concrete Buildings

The fundamentals of the seismic resilience and evaluation method are presented. The evaluation is based on a non-dimensional analytical function for loss variation and a linear recovery function for a community in an average state of preparedness within a specified 'recovery period'. The loss function is a normalized function where the drop of functionality right after the extreme event. The formulated framework, applied for a complex system of six hospitals (considering direct and indirect losses), is employed for low and medium-rise retrofitted reinforced concrete buildings in which the seismic performance has been evaluated by the displacement-based design method. Although this type of design prevents loss of people life it cannot maintain functionality or limit damages. A newly developed Resilience-Based Earthquake Design is promising to address these demands. This research shows that the FRP retrofit is more effective than steel bracing in terms of improving performance and ductility in low-rise RC buildings and the measuring seismic resilience shows an enhanced value as opposed to the un-retrofitted structure

Performance based assessment of FRP-retrofitted existing RC frames

In recent years, performance based design has become universally acceptable in seismic assessment of structures. Using this design method, performance of existing and retrofitted RC buildings can be evaluated based on the criteria suggested by ATC-40 and FEMA-356 using nonlinear pushover analysis. In this paper, performance of an FRP-retrofitted RC frame is assessed and the result is compared with steel-braced frames and unstrengthened moment resisting frames. The strong-column weak-beam principal is employed in this study. Firstly, the flexural stiffness of FRP-retrofitted joints of an existing RC ordinary moment resisting frame is determined using nonlinear finite element analysis. It is then implemented into a mathematical model for the web-bonded FRP-retrofitted frame developed by the first two authors. Subsequently, the base frame and retrofitted frames (both steel-braced and FRP-retrofitted) are analysed using nonlinear pushover analysis method. Finally, the seismic performance of the FRP retrofitted frame is compared with the corresponding base frame and steel-braced frames reported by others. The results show that the improvement in ductility and performance level of the existing RC frames is better for frames retrofitted with FRPs than the steel-braced systems

Performance vs Resilience-based Earthquake Design for Low and Medium-rise retrofitted RC Buildings

A large number of reinforced concrete (RC) structures designed according to older codes do not satisfy the requirements of new seismic design standards. Current codes design the buildings based on life safety criteria. In a Performance-Based Design (PBD) approach, decisions are made based on demands, such as target displacement, and the performance of the structure in use. This type of design prevents loss of life but does not limit damages or maintain functionality. As a newly developed method, Resilience-Based Earthquake Design aims to maintain functionality of buildings and provide liveable conditions after strong ground movement. In fact, Resilience-Based Design (RBD) can be considered as the next generation of PBD. In this paper, seismic performances of a scaled eight-story frame and two full-scaled low-rise RC frames are evaluated. In order to evaluate the earthquake performance of the frames, the performance points of the two frames are calculated by the Capacity Spectrum Method (CSM) of ATC-40. This method estimates the maximum response of a structure by expressing both structure capacity and the ground motion demand in terms of spectral acceleration and displacement. Finally, the seismic performances of the frames are evaluated and the results are compared with a resilience-based design criterion

Structural Health Monitoring of Older Bridges: Current Studies in Australia and Worldwide

Iron, steel and timber bridges were built extensively in the last half of the 19th and early part of the 20th Century. Many of these bridges are now deteriorating and becoming potentially unsafe. There is a need and an opportunity for engineers to analyse the methods and procedures necessary to ensure a responsible balance between structural safety of these bridges, their economy and forward planning for rehabilitation of these bridges. It is difficult to determine the load-carrying capacity of degraded bridges in order to subsequently assess suitable designs for more economic and efficient repairs and maintenance versus replacement. Static load testing has often been the main method to quantify the acceptable load capacity of structures such as timber bridge girders, but it can be expensive. Therefore, there is justification to develop a low-cost, non-destructive evaluation (NDE) that can be used to identify the load-carrying capacity of older bridges in order to identify alternative maintenance and repair strategies. Some attempts in this direction have been made in the past. One of the objectives of Structural Health Monitoring (SHM) is to ensure the safety and reliability of an engineering system for specified functions and loading conditions over a given period of time. Structural safety and reliability become the key issues in the whole process of evaluation. Reliability assessment of the design of structural members and systems has received a great deal of attention by researchers in the last decade and many methods have been developed. A number of selected studies on older bridges in terms of structural health monitoring in Australia and worldwide are presented

Truss Analogy for the Design of FRP- Retrofitted RC Exterior Beam-Column Joints

It is now generally accepted that beam-column joints are critical regions in reinforced concrete (RC) frames designed for inelastic response to severe seismic attack. Inadequately detailed joints, especially exterior ones, have been identified as critical structural elements that may fail prematurely due to high shear stresses [1]. Strengthening of RC joints is a rather difficult task. A variety of techniques have been applied to joints, with the most common being the construction of RC or steel jackets. The rehabilitation of RC columns jacketed with carbon fibre-reinforced plastic (FRP) composites for improving shear strength, confinement, and ductility has received considerable attention in recent years. An extensive test on 18, 2/3 scale exterior joints was carried out by Antonopoulos and Triantafillou [2]. Ghobarah and Said [3], developed design methodology for fibre jacketing to upgrade the shear capacity of existing beam-column joints in RC moment resisting frames. Smith and Shrestha [4] carried out a concise but systematic review of experimental research on the strengthening of RC connections with FRP in addition to an evaluation of the effectiveness of the strengthening schemes. Smith and Shrestha noted that four different types of deficiencies have been introduced into connections that require strengthening with FRP. These are shear strengthening, anchorage strengthening, shear and anchorage strengthening and plastic hinge relocation. Recently, Shrestha and Smith [5] reported the results of a detailed experimental investigation on the FRP strengthened RC beam-column connections subjected to monotonic loading and compared these results with their proposed analytical model. The aim of this study is to fill the gaps that exist in the current state of knowledge for the FRP strengthening of joints worldwide. In this paper, a truss analogy proposed by Hwang and Lee [6] for unstrengthened exterior beam-column joints has been further developed to cover the shear strength of FRP-strengthened joints. The method is checked against numerical analyses that are calibrated with available experimental results. The numerical analysis is extensive and is performed with the latest version of ANSYS software