Professor Patrick Tang

This paper presents a seismic retrofit method to reinforced concrete structures which suffer from soft-storey mechanism in their ground level. The proposed method consists of strengthening of columns by FRP wraps, and an inclusion of a double, upper toggle-brace-damper system. This method considers functionality and practicality in retrofits of existing structures. Governing equations are examined. It is found that, if designed properly the toggle-brace-damper significantly increases stiffness and effective damping of system.The complete system can be described by a simple, nonlinear single-degree-of-freedom system.

Considering the increasingly complex and interconnected subway tunnels linking cities, this review argues that the overall reliability of tunnel engineering is crucial for protection when subjected to loads caused by major catastrophes, particularly earthquakes. Therefore, the key topic of this paper is the application of the resilience concept for shield tunnel structure seismic resilience assessment. In the review, from the technical perspective of civil engineering, based on the five characteristics of resilience, four aspects regarding the seismic resilience of shield tunnels were presented: failure mode and damage mechanism, seismic design method, prevention measures and post-earthquake repair of shield tunnels. First, the definition of seismic resilience of shield tunnel is introduced. Then the failure modes of the shield tunnel under the seismic action and mechanism of damage were summarised under two types: global and local. Consequently, based on the design, several seismic calculation methods were analysed. Next, the current understanding and exploration of shield tunnels in the construction and repair stages were described. Because of lack of relevant repair cases following earthquakes, this review provides a summary of the newly developed techniques and methods of the shield tunnel, which are used to improve seismic resilience during operation. Further, the limitation of the current research were summarised, followed by a short discussion on improving the resilience of shield tunnels in terms of seismic design, construction, operation, and post-earthquake repairs. The final aim is to develop a robust and suitable tool to enhance and maintain shield tunnel resilience, starting from the weaknesses of the tunnel structure faced with earthquakes.

Silty sand slopes are prone to damage due to seepage or rainfall. A partial reinforcement method using short polypropylene fiber and sand mixtures was proposed to protect silty sand slopes from seepage flow failure. The effects and the reinforcement mechanism were explored. First, triaxial tests were performed on sand samples reinforced with fiber lengths (6 and 12 mm) and contents (0.25 and 0.50%) to verify the reinforcement effect. Then, model tests were conducted on sand slopes under lateral seepage flow and the failure mode with different fiber contents and reinforcement method were examined. The results showed that the cohesion and shear strength of sand were significantly improved with the increase of fiber content and length. The suction of unsaturated sand was also enhanced by the fibers. The change in stress-strain behavior from strain softening to strain hardening indicated that static liquefaction could be effectively prevented. The failure mode and extent of slope damage depended on the fiber content. However, it was noted that the slope surface with small reinforcement range performed similarly to that with large reinforcement range. In conclusion, the partial reinforcement method with short discrete synthetic fibers can be used as an effective alternative for slope reinforcement.

The utilisation of recycled concrete aggregate (RCA) in Self-Compacting Concrete (SCC) has the potential to reduce both the environmental impact and financial cost associated with this increasingly popular concrete type. However, to date limited research exists exploring the use of coarse RCA in SCC. The work presented in this paper seeks to build on the existing knowledge in this area by examining the workability, strength, and fracture properties of SCCs containing 0%, 25%, 50%, 75%, and 100% coarse RCA. The experimental programme indicated that at RCA utilisation levels of 25% to 50% little or no negative impact was observed for strength, workability, or fracture properties, with the exception of a slight reduction in Young's modulus.

During the last decade, self-healing of concrete has attracted so much attention in the research community as a promising tool toward more durable and sustainable infrastructures. Although various self-healing approaches have been vastly studied, employment of different assessment methods in these studies has made it difficult to compare the efficiency of various self-healing mechanisms. This paper presents a review of test methods which have been commonly utilized to assess the efficiency of self-healing mechanisms in concrete. Three broad categories of assessment methods are considered, namely visualization and determination, assessment of regained resistance and assessment of regained mechanical properties. Moreover, as a pathway toward standardized evaluation of self-healing mechanisms, various assessment techniques are evaluated against four proposed essential criteria - reliability, quality of results, operational considerations and in-situ applicability.

© 2014 American Society of Civil Engineers.In this paper, three recycled coarse aggregates (RCAs) with different 24-h water absorptions (5.67, 3.12, and 1.98 wt%) were used to produce recycled coarse aggregate concretes (RCACs). Different water absorption rates were obtained by modifying the surface of RCAs with low and high concentration of alkaline organosilicone modifier that is stable in concrete. A normal aggregate concrete mixture was also prepared to serve as control mixture. The effect of RCA absorption on the microstructure (interfacial transition zone), mechanical properties (compressive strength, modulus of elasticity, and concrete-rebar bonding strength), and durability (shrinkage and water permeability) of the resulting RCAC was investigated. Test results showed that the surface modification of RCA was effective in reducing the water absorption. From micrographs, RCAC prepared with low concentration of surface modifier (No. 2 RCA) showed mechanical interlocking with the surrounding cement matrix. Among RCAC, No. 2 RCA (with low concentration of surface modifier) showed better mechanical and durability performance due to the mechanical interlocking which served as effective force transmission medium between aggregate/cement matrix. It can therefore be concluded that RCA prepared with low concentration of surface modifier improved the properties of RCAC. In addition, it may be used as a potential tool to reduce possible slump loss in fresh concrete thereby resulting in consistent mix and providing greater flexibility in mix design.

This paper presents the results of experimental investigation on macro encapsulated phase change material (PCM) incorporated in concrete walls of room models in real conditions. The focus of this study was to evaluate the effect of positions (externally bonded, laminated within and internally bonded) of macro encapsulated PCM in concrete walls on indoor temperatures and humidity levels of room models. Experimental results indicated that PCM models could adjust the indoor temperature and humility levels, however, its effectiveness was found to be greatly dependent on the position of PCM in concrete walls. The model with PCM laminated within the concrete walls showed the best temperature control and was effective in reducing the maximum temperature by up to 4 C. Whereas, the model with PCM placed on the inner side of concrete walls showed the best humidity control and reduced the relative humidity by 16% more than the control model. Therefore, it can be concluded that PCM models are thermally efficient and by reducing the relative humidity they provide comfortable and healthy indoor environment. Moreover, it is shown that the application of PCM in public housing flat of Hong Kong is economically visible with a recovery period of 11 years. © 2013 Elsevier B.V.

In this paper, a method of aggregate surface modification using cement paste with RLP (Redispersable Latex Powder) was proposed aiming to improve properties of recycled aggregates and the resulting concrete. In this study, the cement pastes with different dosages of RLP on RA surface modification were used and the effects on the mechanical properties of the resulting concretes were studied. The experiments were carried in accordance with specifications and test methods in Building pebble and gravel (GB/T 14685-2001) and Ordinary concrete mechanics performance test method standard (GB/T 50081-2002). The test results showed that the properties of recycled aggregates were not as good as those of natural aggregates, thus resulting in poorer mechanical properties of the recycled aggregate concrete. By means of aggregate surface modification, the values of water absorption of the recycled aggregate were reduced and consequently the mechanical properties (i.e. compressive strength and elastic modulus) of the resulting recycled concrete were increased. This research provides some useful practical insights to improving mechanical properties of recycled aggregate concrete. © (2013) Trans Tech Publications, Switzerland.

Fibre reinforced polymer (FRP) materials are currently used for concrete structures in areas where corrosion problems are serious. Recent applications of FRP rebars in normal reinforced concrete structures in fact cannot fully utilise the strength of FRP. A more rational use of FRP would be in the area of prestressed concrete (PC) structures. In spite of the superb strength provision of FRP tendons over steel tendons, use of FRP PC members is often questioned by practising design engineers. This is largely due to the brittleness of FRP tendons and lack of ductility in FRP RC structures. Recent research has demonstrated some important findings in promoting the confidence of adopting FRP RC beams. This paper reviews some recent work on the use of FRP in PC structures. Future possible research areas are also highlighted. © 2003, MCB UP Limited

This paper presents an overview and discusses the applications of fibre reinforced polymer (FRP) bars as reinforcement in civil engineering structures. Following a discussion of the science underpinning their use, selected case studies where FRP reinforcement has been used are presented. The use of FRP reinforcement is rapidly gaining pace and may replace the traditional steel due to its enhanced properties and cost-effectiveness. In addition, FRP reinforcement offers an effective solution to the problem of steel durability in aggressive environments and where the magnetic or electrical properties of steel are undesirable. © 2002, MCB UP Limited

The inclusion of pozzolans like pulverised fuel ash (PFA), silica fume (SF) and metakaolin (MK) enhances the properties of concrete both in fresh and hardened states. In the case of high performance concrete (HPC), their role in enhancing the workability, strength and durability is extremely significant. However HPC has been observed to be more vulnerable than normal strength concrete when exposed to elevated temperatures. This paper presents an overview and discusses the strength and durability performance of high-performance pozzolanic concretes incorporating PFA, SF, and MK subjected to elevated temperatures. Various researchers have demonstrated that addition of silica fume causes HPC to perform poorly when subjected to elevated temperatures. Higher loss of strength and spalling risks are also associated with it. Addition of PFA and MK has been found to improve the fire performance of HPC both in terms of residual strength and durability. © 2002, MCB UP Limited

On 29th January 2010, a tragedy took place before the blissful Chinese Lunar New Year. An old tenement building in Ma Tau Wai collapsed in a sudden, causing 2 deaths and 4 injuries. Not only did this raise people's concerns to investigate the reasons the collapse of the tenement building, it also raised their awareness on old tenement buildings as well as protecting them from collapsing. In view of this, this paper investigates on condensation and how it might shorten the service life of that old tenement building. © (2014) Trans Tech Publications, Switzerland.

The adhesive attachment of FRP materials to the external face of reinforced concrete structures is currently one of the most popular methods in the research community for retrofitting and strengthening concrete structures. Although there is an enormous potential for the use of FRP materials in this area, their large-scale implementation is often impeded by the lack of data on their durability performance. This study investigates and compares the behavior of the bond between FRP materials and concrete in various bonding systems under fatigue conditions. The FRP bond systems studied include externally bonded FRP (EB-FRP), near-surface mounted FRP (NSM-FRP), fiber anchored FRP (FB-FRP), and a newly developed hybrid bonded FRP system (HB-FRP). In the HBFRP system, the mechanical fastener was fixed in two conditions, and therefore a total of five groups of bonding systems were studied. To achieve the objectives of the study, an improved double-face shear type bond test (direct pullout test) was developed. The influence of the load amplitude and number of cycles on the bond performance is scrutinized and discussed through analyzing the failure mechanism, load-slip curves, and strain measurements taken during both the fatigue and monotonic tests. Based on the test results, the advantages and disadvantages of different bond systems are discussed in terms of the fatigue bond performance.