Zubair Imam Syed

Shear Failure of RC Dapped-End Beams

Reinforced concrete dapped-end beams (RC-DEBs) are mainly used for precast element construction. RC-DEBs generally are recessed at their end parts and supported by columns, cantilevers, inverted T-beams, or corbels. The geometric discontinuity of dapped-end beams evokes a severe stress concentration at reentrant corners that may lead to shear failure. Therefore, stress analysis is required at the reentrant vicinity for design requirement of these beams. Four large-scale RC-DEBs specimens were prepared, cast, and tested up to failure. Three parameters were investigated: amount of nib reinforcements, main flexural reinforcements, and concrete type at the dapped-end area. Finite element analysis using Vec2 was also conducted to predict the behavior of RC-DEBs. It has been found that highest stresses concentration factors occur at the reentrant corners and its vicinity. By using engineered cementitious composite (ECC) in the dapped-end area, the failure load has increased by 51.9%, while the increment in the failure load was 62.2% and 46.7% as the amount of nib reinforcement and main flexural reinforcement increased, respectively. In addition, Vec2 analysis has been found to provide better accuracy for predicting the failure load of RC-DEBs compared to other analysis approaches.

Single-Degree-of-Freedom Based Pressure-Impulse Diagrams for Blast Damage Assessment

Pressure-impulse (P-I) diagrams, which relates damage with both impulse and pressure, are widely used in the design and damage assessment of structural elements under blast loading. Among many methods of deriving P-I diagrams, single degree of freedom (SDOF) models are widely used to develop P-I diagrams for damage assessment of structural members exposed to blast loading. The popularity of the SDOF method in structural response calculation in its simplicity and cost-effective approach that requires limited input data and less computational effort. The SDOF model gives reasonably good results if the response mode shape is representative of the real behaviour. Pressure-impulse diagrams based on SDOF models are derived based on idealised structural resistance functions and the effect of few of the parameters related to structural response and blast loading are ignored. Effects of idealisation of resistance function, inclusion of damping and load rise time on P-I diagrams constructed from SDOF models have been investigated in this study. In idealisation of load, the negative phase of the blast pressure pulse is ignored in SDOF analysis. The effect of this simplification has also been explored. Matrix Laboratory (MATLAB) codes were developed for response calculation of the SDOF system and for repeated analyses of the SDOF models to construct the P-I diagrams. Resistance functions were found to have significant effect on the P-I diagrams were observed. Inclusion of negative phase was found to have notable impact of the shape of P-I diagrams in the dynamic zone.

Evaluation of Nano-Silica Modified ECC Based on Ultrasonic Pulse Velocity and Rebound Hammer

To facilitate the usage of the NS-ECC in the construction industry, using nondestructive tests such as rebound hammer (RH) and ultrasonic pulse velocity (UPV) to predict the compressive strength of NS-ECC is worthwhile. Twenty mixtures with two variables which are four PVA% (0.5, 1, 1.5 and 2) and five NS% (0, 1, 2, 3 and 4) have been proportioned, cast, cured and tested using RH, UPV and then crushed to determine the compressive strength at age of 28 days.

Prediction of Failure Loads of RC Dapped-End Beams

Shear failure remains the governing mode of failure for reinforced concrete (RC) dapped-end beams. Dapped-ends are commonly classified as disturbed regions (D-regions). Strut and tie model (STM) is a simple and rational way that can be applied to analyze D-regions. The current design codes such as ACI-318-08, Euro Code 2 and BS 8110 facilitate STM to predict the failure loads. In addition, the failure loads may be also predicted using the empirical method proposed in PCI Design Handbook. In this paper, the failure loads were predicted for 24 RC dapped-end beams following different codes. The significant parameters such as concrete compressive strength, dapped-end section size, shear span-depth ratio, type and effective range of stirrups, bent form of the longitudinal reinforcement, amount of dapped-end reinforcements and hanger reinforcements were varied to study their effects against the predicted failure load for RC dapped-end beams according to different codes. These predicted results were compared with the available experimental results to investigate the ability of various codes to predict the failure load reliably. In this study, the comparison shows that PCI Design Handbook and ACI-318-08 can predict the failure loads for RC dapped-end beams more accurately.

Broadside Vessel Collision Forces for Conventional Riser-Guard

Oil and gas operators have taken considerable amount of measures to prevent offshore service vessel collision with risers, especially in the wake of the Mumbai High North disaster. One of the measures taken is the installation of steel riser-guards on fixed offshore jacket platforms. The conventional riser-guard however, has been associated with several design related issues, which provide room for further design optimisation, or even a potential replacement with other alternatives. Quantification and selection of appropriate design load for riser-guard system is highly desirable for design improvement and optimization. This study attempts to investigate and establish the impulse loads equivalent to the broadside collision of a 2500 tonne displacement vessel with the conventional riser-guard. Parametric study was performed to investigate the effects of varying width to the resulting impulse load equivalent to vessel collision forces. General purpose finite element modelling software was used to perform dynamic analysis and establish the equivalent impact loads.

A Review on Composite Materials for Offshore Structures

Research into advanced composite materials for offshore structures is growing due to factors such as new challenges in extreme environments, contaminated contexts (chemical, biological) and increasing awareness of earthquake risks. Advances in theory and practice of composites technology have modified the general perception of offshore structures. This paper provided an introduction to composite material and reviewed the application of composites in offshore structures. This survey focused on (1) composites, especially FRP, for repairing offshore structures and also (2) fire protection of composites in offshore structures. Various national and international research projects on uses of composites for marine structures either ongoing or completed during last decades summarized. Future environmental issues considered and eco-friendly sustainable composite suggested and forecasted for new generation of offshore structures.Copyright

Performance of Simplified Damage Assessment Tools for Reinforced Concrete Panels under Blast Loading

Pressure-impulse (P-I) and charge weight-distance (CW-D) diagrams are widely used as quick damage assessment tools for reinforced concrete (RC) elements exposed to blast loading. Depending on the loading and element properties, the blast loading can induce different patterns of response and damage. Appropriate application of different simplified damage assessment tools for both far-field and near-field blast effects can be significantly challenging. This paper presents the comparison of the performances of two commonly used simplified damage assessment methods for RC elements exposed to explosive loading. Different aspects of the simplified damage assessment methods related to their construction and application for damage assessment are investigated. Some specific limitations of construction and use of P-I and CW-D diagrams are explored. Suitability of P-I diagrams for far-field and near-field blast effects is also explored. P-I diagrams are found to provide misleading damage assessment when applied for near-field blast effects.

Curvature Ductility of Concrete Element under High Strain-Rates

Considerable amount of studies on the ductility and flexural behaviour of normal and high strength concrete elements under static load can be found in literature. However, most of the previous theoretical investigations on moment-curvature (M-φ) relationship of concrete elements to calculate curvature ductility and flexural capacity did not take account of the strain-rate effect on the material models. M-φ analysis of concrete elements under dynamic loading are often conducted with material models developed for quasi-static load by applying Dynamic Increase Factors (DIF) to the material properties to reflect the strain-rate effect. Depending on magnitude and duration of applied dynamic load, element stiffness and boundary condition strain-rate varies over the cross section. Thus, the application of DIF to modify peak material properties often fails to reflect the strain-rate effect reliably. The improvement of using material model which incorporated strain-rate in its constitutive equations has been explored in this study. The effects of reinforcement amount, grade and concrete strength on curvature ductility for different strain rates have been studied using material models which have strain-rate effects included in theirs formulation. Based on the parametric study, a simple formula to estimate curvature ductility for concrete elements under explosive loads (high strain-rates) has been proposed.