Abstract: Ultra-high performance cementitious composite (UHPCC) with 200MPa compressive strength was prepared by substitution of ultra-fine industrial waste powder for 60% cement by weight. Compressive impact behaviour of UHPCC with different fiber volume fraction was researched by split Hopkinson pressure bar in four kinds of impact modes. Standard strength of UHPCC under impact was defined. The effects of strain rate, impact times, impact modes and fiber volume fraction on the properties of UHPCC under impact were researched. Results showed that impact resistance of UHPCC was improved with the increase of fiber volume fraction. With the increase of strain rate the dynamic strength of UHPCC was improved. With the increase of impact times the damage of material increased while the standard strength decreased. With the change of impact modes the damage of material on the first impact and the rate of the reduction of peak stress on the second and third impact increased. After a long time freezing-thaw cycle, corrosion and carbonation, results indicated that UHPCC had excellent durability.
Abstract: This paper presents the theory and practice of new types of long-span building structures developed at Guizhou University for the recent 25 years. The new structural systems include RC open-web sandwich plate structures, steel/RC composite open-web sandwich plate structures, prestressed RC open-web sandwich plate structures, and cast-in-place concrete round eye hollow plate structures. The mechanical characters and technical indexes of each system are described. The application of the structures is detailed in tables and photos.
Abstract: Recent advancements in concrete science and technology have made possible the development of high performance fiber reinforced cementitious composites (HPFRCC) with excellent mechanical properties and long-term durability. However, the costs of these materials are many times that of conventional concrete and the construction of complete structures with them is hard to justify. The strategic application of high performance materials, in selected parts of concrete structures, can bring along higher performance/cost and wider acceptance of the material in practice. This paper will investigate several examples of selective HPFRCC application, including the fabrication of permanent formwork for durability enhancement, the replacement of steel reinforcements at the anchorage zone of post-tensioned members to relieve the steel congestion problem as well as the development of simple and narrow joints for pre-cast concrete members. Based on the experimental results obtained so far, the selected use of HPFRCC in concrete structures appears to have good potential for practical applications.
Abstract: In this paper, the steel plate-concrete composite (SPCC) beam is developed, in which traditional steel beam in the steel-concrete composite beam is replaced by a steel plate. The aim to develop this type of composite beam is to provide a theoretical basis for design of SPCC structures and SPCC-strengthened structures. In order to investigate the flexural behavior of SPCC beams, tests were conducted on five specimens with loading cases of four-point or three-point bending. All the beams were identical in geometry, longitudinal reinforcement, stirrup, and concrete strength but various in steel plate thickness, shear connection degree, shear span length and cut-off position of steel plate. The structural behavior of the tested SPCC beams, including strain, deflection, crack width, load carrying capacity and deformability, etc., were measured and analyzed. Based on test results, it can be concluded that by means of appropriate shear connection degree and anchorage length, steel plate and concrete can work together very well and the SPCC beams have a very good ductility. The ultimate strength of the SPCC beams can be calculated by means of the same plastic method as reinforced concrete beams.
Abstract: Ultra-high toughness cementitious composite (UHTCC) exhibits the pseudo-hardening feature when subjected to tensile load and has high tensile strain capacity of normally up to 3%. Also, UHTCC has a unique cracking behavior. From cracking up to ultimate tensile strain capacity, the crack width in UHTCC could be still kept below 100m. This paper presents the utilization of UHTCC to replace a layer of concrete surrounding the main flexural reinforcement in ordinary RC beam to improve flexural performance especially beam durability as UHTCC displays high toughness and shows multiple fine cracks. Analytical closed-form formulae for flexural capacity, curvature and deformation of UHTCC/RC composite beam derived based on the elastic beam theory is presented first. Subsequently, experimental results of two groups of different reinforcement ratios of UHTCC/RC beams and control RC beams tested under flexural loading to verify the feasibility of analytical formulae as well as to examine the performance improvement of UHTCC/RC composite beam over the control beam is presented. Moment-curvature curves and load-mid span displacement curves for the tested beams are compared with the theoretical analysis. A good agreement between experimental and analytical results is found. The experimental results show that the use of a layer of UHTCC in RC beams can enhance both flexural capacity and ductility. The improvement is not significant with the increase in reinforcement ratio; however, the maximum crack width under service load even in the case of lightly reinforced beams can be limited within 0.1mm.
Abstract: In this paper the new Italian seismic code issued in January 2008 is presented, with particular reference to the ample section devoted to constructions built with isolation and energy dissipation systems. Such attention is justified by the undisputed effectiveness of this design approach and by its increasing diffusion in the professional community. The code is based on Eurocode 8 , though resulting more synthetic and easier to use. During the last years of evolution, the code has significantly contributed to the development of new concepts in seismic isolation, such as the hybrid biaxial isolating/dissipating device here presented, obtained from parallel coupling of two different types of device: one mechanical, which realizes the necessary dissipation, and one elastomeric, which has the scope, beyond that of sustaining the vertical load, of reducing the deck residual displacement at the end of the seismic action. An application is shown of a seismically retrofitted highway bridge, in order to show the effectiveness of this device, both during, in terms of isolation, and at the end of the seismic event, in terms of residual displacements. For the sake of comparison, the same bridge is analyzed with different types of isolation techniques.
Abstract: Smart concrete technology provides a new alternative way for health monitoring of reinforced concrete structures. In this paper, the piezoresistivity of two kinds of smart concrete filled with carbon black or carbon fiber was studied, and two types of embedded sensors were fabricated using the smart concrete with favorable piezoresistivity. The sensing performance, the measuring methods and the response to environmental temperature and humidity of embedded sensors were investigated. A compensation circuit was incorporated to reduce the effect of temperature and humidity on the output of embedded sensors. The sensors were embedded in concrete beams and columns to monitor the structural compressive strain under field conditions. Experimental results indicate that the embedded sensors fabricated using smart concrete filled with carbon black or carbon fiber feature favorable sensing performance (gauge factors are 55.28 and 138 respectively). The self-sensing concrete components embedded with these sensors can realize the monitoring of their local compressive strain. It therefore can be concluded that the prepared smart concrete and the developed embedded sensors have great potential to be used for health monitoring and damage assessment of concrete structures.