Construction mediation and its hybridization: the case of the Hong Kong construction industry

In view of the sophisticated nature of construction disputes, specialized dispute resolution mechanisms are of pivotal importance to the satisfactory settlement between disputing parties. Among the various construction dispute resolution mechanisms, mediation has been increasingly gaining recognition and acceptance. Its hybrid, namely mediation-arbitration (med-arb), has also emerged and has started receiving attention and appreciation. With special reference to the construction industry practice in Hong Kong, a commentary on the respective merits and demerits of construction mediation and construction med-arb, as well as the ways forward, are presented in this article

Development of Sustainable High-Strength Self-Consolidating Concrete Utilising Fly Ash, Shale Ash and Microsilica

With high flowability and passing ability, self-consolidating concrete (SCC) does not require compaction during casting and can improve constructability. The favourable properties of SCC have enabled its widespread adoption in many parts of the world. However, there are two major issues associated with the SCC mixes commonly used in practice. First, the cement content is usually at the high side. Since the production of cement involves calcination at high temperature and is an energy-intensive process, the high cement content imparts high embodied energy and carbon footprint to the SCC mixes. Besides, the exothermic reaction of cement hydration would cause high heat generation and early thermal cracking problem that would impair structural integrity and necessitate repair. Second, the strength is usually limited to around grade 60, which is considered as medium strength in nowadays achievable norm. With a view to develop sustainable high-strength self-consolidating concrete (HS-SCC), experimental research utilising fly ash (FA), shale ash (SA), and microsilica (MS) in the production of SCC has been conducted, as reported herein

Tension-stiffening behaviour of reinforced concrete ties of various strength classes

A new law of tension-stiffening for reinforced concrete (RC) ties is proposed in the present study. It is based on the test data of 11 experimental programs of RC elements of various strength classes reported in the literature. The experimental programs covered a wide range of characteristics of mechanical and geometrical parameters of specimens such as compressive strength of concrete, reinforcement ratio and diameter of reinforcement bars. By eliminating the effect of shrinkage from the test load-strain diagrams of the ties, a simple model with no dependence on reinforcement ratio could be derived. The proposed tension-stiffening law is compared with the formulation in Eurocode 2. Statistical analysis of strain predictions of RC ties based on Eurocode 2 was conducted. It is found that the Eurocode 2 significantly underestimated strains in the RC ties with the errors reaching 50% for the lightly reinforced members. Nevertheless, when shrinkage effect was accounted for in the test load-strain diagrams, the predictive capability of the Eurocode 2 formulation could be significantly improved

Experimental and Numerical Analysis of Strain Gradient in Tensile Concrete Prisms Reinforced with Multiple Bars

This work is a continuation of the ongoing research on deformation behavior of reinforced concrete elements under tension. The previous studies have revealed that deformation behaviors of elements reinforced with multiple bars and the traditional prismatic members reinforced with a center bar are essentially different. The latter layout, though typical of laboratory specimens, could not represent the norm of structures in real-life. Thus, a new test methodology to investigate the strain distribution in concrete prismatic members reinforced with multiple bars subjected to axial tension is devised. Prismatic concrete specimens with different reinforcement configurations were fabricated and tested using the proposed setup. Deformation behavior of the specimens is modeled with a tailor-designed bond modeling approach for rigorous finite element analysis. It is revealed that the average deformations of the concrete could be different from the prevailing approach of average deformations of the steel, and are dependent on the reinforcement configurations. Therefore, the efficiency of concrete in tension should be carefully taken into account for rational design of structural elements. The study endorses promising abilities of finite element technique as a versatile analysis tool whose full potential is to be revealed with the advent of computer hardware

Predicting crack spacing of reinforced concrete tension members using strain compliance approach with debonding

A novel technique based on strain compliance for investigating the crack spacing of reinforced concrete (RC) tension members has been developed. The new method is based on the mean strain and the partial interaction (stress-transfer) approaches. The strain compliance principle is established by equating together the mean strains of a reinforced concrete block between adjacent primary cracks estimated by the mean strain and the stress-transfer approaches. The distribution of reinforcement strains within the RC block must be known to apply the stress-transfer approach. This technique is intended for the stabilized cracking stage, where formation of new primary cracks has ceased. This work accounts for local effects – fully damaged bond between the concrete and reinforcement near the cracks. Knowledge of a benchmark data point obtained from a reference element is required. The point is defined by the reinforcement ratio, bar diameter and mean crack spacing values. This data point enables the estimation of the mean crack spacing for other RC tension elements. A comparative investigation was carried out, with two different mean strain approaches, following the free-of-shrinkage tension stiffening law and provisions in Eurocode 2. The obtained results provide reasonably accurate estimates of crack spacing compared to experimental values

Challenges of regulatory theory and practice : a study of hawker control in Hong Kong

published_or_final_versionPolitics and Public AdministrationMasterMaster of Public Administratio

Nonlinear multilevel analysis of reinforced concrete frames

Full range analysis of reinforced concrete (RC) members covering the post-crack and post-peak regimes is important for obtaining the deformation response and failure mode of structural members. When a RC member is subject to an increasing external load, the critical sections would exhibit cracking and/or softening. Due to stress relief effect in the proximity of crack opening and plastic hinging, unloading may occur at the adjacent regions. The variable stress states of discrete sections would lead to sectional variation of stiffness, which could not be accounted for by conventional structural analysis methods. In this paper, a nonlinear multilevel analysis method for RC frames whereby the frame members are divided into sub-elements and sectional analysis is utilised to evaluate stiffness degradation and strength deterioration is developed. At sectional level, the secant stiffness is determined from moment-curvature relation, where the curvature is evaluated based on both transverse displacements and section rotations of the frame member. Unloading and reloading behaviour of concrete and reinforcing steel is simulated. In implementing the multilevel analysis, secant iteration is performed in each step of displacement increment to obtain the convergent solution satisfying equilibrium. Numerical example of RC frame is presented to demonstrate the applicability and accuracy of the proposed nonlinear multilevel analysis method

Effect of concrete stress states on carbonation depth of concrete

Carbonation can lead to reduction of alkalinity of concrete and initiation of steel reinforcement corrosion. In durability design of concrete structures, the carbonation depth should be duly considered. However, the concrete stress state would influence the carbonation depth, and there has been inadequate research on such effect. In this study, it is proposed to introduce a stress influence coefficient to the concrete carbonation depth model. With reference to the experimental data from eleven research studies in the literature encompassing both tensile and compressive stress states, the relationship between stress influence coefficient and concrete stress ratio is quantitatively investigated, and mathematical equations relating the stress influence coefficient with the concrete stress ratio are established. Comparative study with three typical existing groups of equations shows that the proposed equations of stress influence coefficient are more reasonable and have a higher reliability. The effects of carbonation time, mix proportions of concrete on stress influence coefficient are also analysed, and the magnitudes of the effects are found to be approximately within ±10%. Finally, the modified carbonation depth models are proposed and verified by the experimental data, which suggests that the proposed models are of desirable accuracy. Adoption of the proposed equations as the modified formula of stress influence coefficient in the concrete carbonation depth model for practical applications is recommended

Modelling chloride diffusion in concrete with influence of concrete stress state

Under coastal or marine conditions, chloride erosion is the major accelerating factor of reinforcement corrosion. Therefore, it is of vital importance to investigate the chloride diffusion model. Research reveals that the concrete stress state has great influence on chloride diffusion; therefore a stress influence coefficient was incorporated in chloride diffusion coefficient model by many researchers. By referring to the experimental data from eight different researchers, the law between stress influence coefficient and concrete stress ratio is studied in detail, and equations relating the stress influence coefficient with the concrete stress ratio are established. Compared with three typical existing groups of equations, it is found that the proposed equations give the most accurate estim.ation of the stress influence coefficient. Hence, the proposed equations can be adopted to improve the valuation of chloride diffusion coefficient, and a modified chloride diffusion model is put forward. Three groups of experimental data are used to validate the modified chloride diffusion  model, which is shown to be reasonable and having high prediction accuracy