Rehabilitation of timber bridge piles using a wrapping system

The majority of the thousands of timber bridges around Australia are more than 50 years old and strengthen-ing and rehabilitation of deteriorated timber bridges is a strong financial commitment. Therefore it is a timely concern to investigate the rehabilitation process involved. The maintenance cost of timber bridges are affect-ed significantly by a number of deterioration mechanisms, which require a systematic approach for diagnosis and treatment. The techniques used to rehabilitate timber bridges vary depending on the deterioration mecha-nism and location. This research aims at investigating the techniques used in timber pile rehabilitation. The main deterioration mechanism studied in this research is the splitting. An experimental program was carried out to investigate the strength enhancement due to a FRP wrapping system combined with two types of filler material, Crane Rail Grout (CRG) and Underwater Cementitious Grout (UCG). Hardwood timber of grade F27 with 150 mm diameter and 300 mm high samples were used in the testing program. Three levels of dam-age were introduced to the total height, samples were wrapped with FRP system and tested for compression. Load and displacement curves were developed based on the experimental results

Structural evaluation of concrete expanded polystyrene sandwich panels for slab applications

Sandwich panels are being extensively and increasingly used in building construction because they are light in weight, energy efficient, aesthetically attractive and can be easily handled and erected. This paper presents a structural evaluation of Concrete-Expanded Polystyrene (CEPS) sandwich panels for slab applications using finite element modeling approach. CEPS panels are made of expanded polystyrene foam sandwiched between concrete skins. The use of foam in the middle of sandwich panel reduces the weight of the structure and also acts as insulation against thermal, acoustics and vibration. Applying reinforced concrete skin to both sides of panel takes the advantages of the sandwich concept where the reinforced concrete skins take compressive and tensile loads resulting in higher stiffness and strength and the core transfers shear loads between the faces. This research uses structural software Strand7, which is based on finite element method, to predict the load deformation behaviour of the CEPS sandwich slab panels. Non linear static analysis was used in the numerical investigations. Predicted results were compared with the existing experimental results to validate the numerical approach used

Experimental investigation on the flexural behaviour of pultruded GFRP beams filled with different concrete strengths

Glass fibre reinforced polymer (GFRP) pultruded profiles are being increasingly used in the construction industry due to their numerous advantageous over the conventional materials. However, most pultruded GFRP sections fail prematurely without utilising their high tensile strength due to their thin-walled sections. As a result, several hybrid systems made out of GFRP profiles and concrete as a filler material have been proposed in order to enhance their structural performance. Most of these studies utilised high strength concrete wherein the additional cost does not justify the enhancement in the stiffness and strength of the infilled GFRP profiles. This paper presents an experimental investigation on the effect of the compressive strength of concrete infill on the flexural behaviour of beams with a view to determine a lower cost infill for GFRP profiles. Pultruded GFRP square beams (125 mm x125 mm x 6.5mm) were filled with concrete having 10, 37 and 43.5 MPa compressive strength and tested under static four-point bending. The results showed that the capacity of the filled beam sections increased by 100 to 141% than the hollow sections. However, the compressive strength of the concrete infill has no significant effect on the flexural behaviour of the beams. The increase in concrete compressive strength from 10 to 43.5 MPa increased the ultimate moment by only 19% but exhibited an almost same flexural stiffness indicating that a low strength concrete is a practical solution to fill the GFRP profile

Analysis of flood impact on reinforced concrete(Pre-stressed) girder bridges – a case study

In recent years, frequencies of flood events in Australia have increased. It is noted that flood events cause the most damage to infrastructure compared to any other natural hazards in the world. Bridge structures located over waterways are prone to failure under flood events. Failure of a bridge can impact on the community significantly by reducing the evacuation capability and recovery operations during and after a disaster. A recent research project commenced at RMIT University aims to examine failure of road bridges under flood events. The paper has reviewed different bridge design codes used over several years in Australia for designing the bridges. Various failure mechanisms of bridges due to flood events have been investigated and the most common failure mechanisms of the bridges in Queensland have been identified by examining bridge inspections conducted after the 2011 and 2013 flood events. A case study bridge, which failed under flood loading, has been modeled and the effects of different flood scenarios have been investigated. The impacts of different types of debris, urban and regional, have also been studied. Damage indices have been derived for a concrete girder bridge to demonstrate the methodology for vulnerability modeling of bridge structures

Predicting the remaining life of timber bridges

This paper documents the current state of knowledge relating to the deterioration of timber bridges in Australia. The aim of this research, was to comprehend the present state of knowledge regarding maintenance of timber bridges and address any gap in knowledge. This involved: identifying key defects in timber, investigat-ing the inspection methods utilised to detect these faults and finding the preven-tive measures used to mitigate bridge deterioration. Enclosed are figures which demonstrate how simple industry practices and procedures implemented by each states’ governing authority can reduce these impacts and concludes with an em-pirical model for predicting the remaining lifespan of a bridge

Floodway Design Process Revisted

Floodways are small road structures that are meant to be overtopped by floodwater during a flood event with relatively low average recurrence interval and expected to be in complete functional stage after the flood water recedes. The severity of 2011 and 2013 flood events in Queensland damaged the floodways in the state causing a huge impact mainly to the rural community during the recovery and rehabilitation stage. Therefore, the resilience of these small critical road structures is of great importance for the survival, safety and recovery stages during such events. Using a case study region in Lockyer Valley Regional Council area, the authors found that majority of the structural damage was caused due to the heavy impact load from the boulders/logs that came with the flood water. Another aspect reviewed was the damage sustained by floodway aprons due to excessive debris loading. This is of particular concern since aprons are the most expensive component of a floodway to repair or replace. Since floodways encounter many forces throughout their service life thorough review and investigation of current design standards are required in order to improve floodway resilience. In an attempt to develop a floodway design process, this paper focusses on the analysis of two types of floodways and reports the procedure used to develop design charts. Detailed finite element analysis is demonstrated by using one type of floodway. Finally, the contribution that resulted from the structural analysis is linked with the current floodway design guide

Behavior of pultruded multi-celled GFRP hollow beams with low-strength concrete infill

The structural performance of multi-celled GFRP hollow beams is highly affected by the local buckling failure. Therefore, this study introduces pultruded multi-celled GFRP beams filled with low strength concrete. The flexural behaviour of beams made up of 1, 2 and 3 pultruded GFRP square sections (125 mm x125 mm x 6.5mm) and filled with concrete having low compressive strength was investigated. The composite beams were subjected to four-point static bending test to determine the strength, stiffness and failure mechanisms. The results of the experimental investigations showed that the failure stress of 2 and 3 cells beams is 98% and 85% compared with single cell beam, respectively. However, the filling percentages are 50% and 33%, respectively. All the tested beams were failed due to compression failure of the GFRP profile. Furthermore, the effective stiffness of 2 and 3 cells is 95% and 96%, respectively compared with single cell section

Deriving damage indices for concrete girder bridges subjected to flood loading

It is noted that the intensity and frequency of disasters have increased over the past few decades and the damage to infrastructure after a natural hazard has consequently increased. The recent flood events in Queensland, Australia had an adverse effect on the country’s social and economic growth. Due to climate change impacts, it is reported that the frequency and intensity of flood events have increased noticeably in recent years. Failure of transport infrastructure after a flood event significantly affects the community, road authorities and wider stakeholders. Bridge structures are often vulnerable to flood events due to their proximity to water ways and the resultant direct impact of flood on structures. In identifying strengthening needs for vulnerable bridge structures, a damage, flood intensity relationship is required. The paper has reviewed different bridge design codes used over several years in Australia for designing the bridges and the method of design for flood loading is identified. Various failure mechanisms of bridges due to flood events have been investigated through analysis of case studies and the most common failure mechanisms of the bridges in Queensland as the result of the 2011 and 2013 flood events have been identified. A case study bridge has been modelled using the general purpose finite element software, ANSYS. The damage to bridges due to impact of floating items under different flood scenarios have been investigated. Damage curves have been generated for the case study bridge under different flood intensities

Design of Alkali-Activated Slag-Fly Ash Concrete Mixtures Using Machine Learning

So far, the alkali activated concrete has primarily focused on the effect of source material properties and ratio of mix proportions on the compressive strength development. A little research has focused on developing a standard mix design procedure for alkali activated concrete for a range of compressive strength grades. This study developed a standard mix design procedure for alkali activated slag‒fly ash (low calcium, class F) blended concrete using two machine learning techniques, Artificial Neural Networks (ANN) and Multivariate Adaptive Regression Spline (MARS). The algorithm for the predictive model for concrete mix design was developed using MATLAB programming environment by considering the five key input parameters; water/solid ratio, alkaline activator/binder ratio, Na-Silicate /NaOH ratio, fly ash/slag ratio and NaOH molarity. The targeted compressive strengths ranging from 25–45 MPa (3.63–6.53 ksi) at 28 days were achieved with laboratory testing, using the proposed machine learning mix design procedure. Thus, this tool has the capability to provide a novel approach for the design of slag-fly ash blended alkali activated concrete grades matching to the requirements of in-situ field constructions

The Evaluation of a Rapid In Situ HIV Confirmation Test in a Programme with a High Failure Rate of the WHO HIV Two-Test Diagnostic Algorithm

BACKGROUND: Concerns about false-positive HIV results led to a review of testing procedures used in a Médecins Sans Frontières (MSF) HIV programme in Bukavu, eastern Democratic Republic of Congo. In addition to the WHO HIV rapid diagnostic test algorithm (RDT) (two positive RDTs alone for HIV diagnosis) used in voluntary counselling and testing (VCT) sites we evaluated in situ a practical field-based confirmation test against western blot WB. In addition, we aimed to determine the false-positive rate of the WHO two-test algorithm compared with our adapted protocol including confirmation testing, and whether weakly reactive compared with strongly reactive rapid test results were more likely to be false positives. METHODOLOGY/PRINCIPAL FINDINGS: 2864 clients presenting to MSF VCT centres in Bukavu during January to May 2006 were tested using Determine HIV-1/2 and UniGold HIV rapid tests in parallel by nurse counsellors. Plasma samples on 229 clients confirmed as double RDT positive by laboratory retesting were further tested using both WB and the Orgenics Immunocomb Combfirm HIV confirmation test (OIC-HIV). Of these, 24 samples were negative or indeterminate by WB representing a false-positive rate of the WHO two-test algorithm of 10.5% (95%CI 6.6-15.2). 17 of the 229 samples were weakly positive on rapid testing and all were negative or indeterminate by WB. The false-positive rate fell to 3.3% (95%CI 1.3-6.7) when only strong-positive rapid test results were considered. Agreement between OIC-HIV and WB was 99.1% (95%CI 96.9-99.9%) with no false OIC-HIV positives if stringent criteria for positive OIC-HIV diagnoses were used. CONCLUSIONS: The WHO HIV two-test diagnostic algorithm produced an unacceptably high level of false-positive diagnoses in our setting, especially if results were weakly positive. The most probable causes of the false-positive results were serological cross-reactivity or non-specific immune reactivity. Our findings show that the OIC-HIV confirmation test is practical and effective in field contexts. We propose that all double-positive HIV RDT samples should undergo further testing to confirm HIV seropositivity until the accuracy of the RDT testing algorithm has been established at programme level