Thermal-creep analysis of concrete bridges

The creep effects on sequentially built bridges are analysed by the theory of thermal creep. Two types of analysis are used: time dependent and steady state. The traditional uniform creep analysis is also introduced briefly. Both simplified and parabolic normalising creep-temperature functions are used in the analysis for comparison. Numerical examples are presented, calculated by a computer program based on the theory of thermal creep and using the displacement method. It is concluded that different assumptions within thermal creep can lead to very different results when compared with uniform creep analysis. The steady-state analysis of monolithically built structures can serve as a limit to evaluate total creep effects for both monolithically and sequentially built structures. The importance of the correct selection of the normalising creep-temperature function is demonstrated.

Test on prestressed concrete beam with AFRP spiral confinement and external aramid tendons

This paper describes an experimental study of a new form of prestressed concrete beam. Aramid Fiber Reinforced Polymers (AFRPs) are used to provide compression confinement in the form of interlocking circular spirals, while external tendons are made from parallel-lay aramid ropes. The response shows that the confinement of the compression flange significantly increases the ductility of the beam, allowing much better utilization of the fiber strength. The failure of the beam is characterized by rupture of spiral confinement reinforcement.

Increasing the design strength of glass – fractography and stress testing

Brittleness is the unintended, but inevitable consequence of producing a transparent ceramic for architectural applications such as the soda-lime glass. Its tensile strength is particularly sensitive to surface imperfections, such as that from natural weathering and malicious damage. Although a significant amount of testing of new glass has been carried out, there has been surprisingly little testing on weathered glass. Due to the variable nature of the causes of surface damage, the lack of data on weathered glass leads to a considerable degree of uncertainty in the long-term strength of exposed glass. This paper presents the results of recent tests on weathered annealed glass which has been exposed to natural weathering for more than 20 years. The tests include experimental investigations using the co-axial ring setup as well as optical and atomic force microscopy of the glass surfaces. The experimental data from these tests is subsequently used to extend existing fracture mechanics-based models to predict the strength of weathered glass. It is shown that using an automated approach based directly on finite element analysis results can give an increase in effective design strength in the order of 70 to 100% when compared to maximum stress methods. It is also shown that by combining microscopy and strength test results, it is possible to quantitatively characterise the damage on glass surfaces.

Magnetic Resonance Imaging of concrete

http://www-civ.eng.cam.ac.uk/cjb/papers/cp88.pdf

Analysis of CFRP strap-strengthened reinforced concrete beams using the modified compression field theory (MCFT)

External, prestressed carbon fiber reinforced polymer (CFRP) straps can be used to enhance the shear strength of existing reinforced concrete beams. In order to effectively design a strengthening system, a rational predictive theory is required. The current work investigates the ability of the modified compression field theory (MCFT) to predict the behavior of rectangular strap strengthened beams where the discrete CFRP strap forces are approximated as a uniform vertical stress. An unstrengthened control beam and two strengthened beams were tested to verify the predictions. The experimental results suggest that the MCFT could predict the general response of a strengthened beam with a uniform strap spacing < 0.9d. However, whereas the strengthened beams failed in shear, the MCFT predicted flexural failures. It is proposed that a different compression softening model or the inclusion of a crack width limit is required to reflect the onset of shear failures in the strengthened beams.

Redundancy quantification in the safety assessment of existing concrete beam-and-slab bridges

In current practice the strength evaluation of a bridge system is typically based on firstly using elastic analysis to determine the distribution of load effects in the elements and then checking the ultimate section capacity of those elements. Ductility of the components in most bridge structures permits local yield and subsequent redistribution of the applied loads from the most heavily loaded elements. As a result a bridge can continue to carry additional loading even after one member has yielded, which has conventionally been adopted as the "failure criterion" in bridge strength evaluation. This means that a bridge with inherent redundancy has additional reserves of strength such that the failure of one element does not result in the failure of the complete system. For these bridges warning signs will show up and measures can be undertaken before the ultimate collapse is happening. This paper proposes a rational methodology for calculating the ultimate system strength and including in bridge evaluation the warning level due to redundancy. © 2004 Taylor & Francis Group, London.

Centrifuge modelling and dynamic testing of municipal solid waste (MSW) landfills

An investigation into the seismic behaviour of municipal solidwaste (MSW) landfills by dynamic centrifuge testing was undertaken. This paper presents physical modelling of MSW landfills for dynamic centrifuge testing, with regard to the following research areas: 1. amplification characteristics of municipal solid waste; 2. tension induced in geomembranes placed on landfill slopes due to earthquake loading; 3. damage to landfill liners due to liquefaction of foundation soil. A model waste, that has engineering properties similar to MSW, is presented. A model geomembrane that can be used in centrifuge tests is also presented. Results of dynamic centrifuge tests with the model geomembrane showed that an earthquake loading induces additional permanent tension (∼25%) in the geomembrane. © 2006 Taylor & Francis Group, London.