Performance of geosynthetic-reinforced flexible pavements in full-scale field trials

The paper presents the results of a series of full-scale trials carried out in Thailand examining the performance of geosynthetics as reinforcement for flexible pavements. The geosynthetics were embedded at different pavement depths and the structural response was monitored across four test sections by means of strain gauges, pressure sensors, deflection points and deflection plates. The results show that all reinforcement configurations helped reduce the vertical static stresses developed at the base of the pavement by up to 66% and by up to 72% for dynamic stresses. The performance enhancement expected to prolong the lifespan of the base layers. The reinforcement layers closer to the base experienced the highest lateral strains of up to 0.13%, providing evidence that geosynthetics can also effectively reduce lateral spreading. All reinforcement configurations helped enhance rut resistance with maximum traffic benefit ratio (TBR) of 13.70, effectiveness ratio (EF) of 12.70 and minimum rutting reduction ratio (RRR) of 0.74. The best configuration included a geotextile within the asphalt concrete layer and a geogrid under the base layer. Non-linear finite element analyses of the test sections predicted very well the strains and stresses in the pavement. The study provides a benchmark for future studies in this field and concludes that geosynthetics can help increase maintenance periods and extend the lifetime of flexible pavements.     

Axial compressive behavior of concrete actively confined by metal strips; part A: experimental study

This paper presents the results of an experimental study on the application of strapping technique for retrofit of concrete compressive specimens. In this technique, standard strapping devices, which are used in the packaging industry, are applied to post-tension high strength metal strips around the concrete columns. Experimental program included axial compressive tests on 72 cylindrical and prismatic compressive specimens, which were actively confined by pre-stressed metal strips. The effects of various parameters on strength and ductility of confined concrete were studied including compressive strength of concrete, mechanical volumetric ratio of confining strips, post-tensioning force in the strip, number of strip layers wrapped around the specimens and details of strip joint. The effects of strength and ductility of confining strips on the behavior of confined specimens were also studied. Longitudinal and lateral strains of concrete and strain of the strips were monitored. Test results showed significant increase in the strength and ductility of specimens due to active confinement by metal strips. It was observed that ductility of confining material plays the most important role in enhancement of concrete ductility. The gain in strength is strongly dependent to the effective mechanical volumetric ratio of confining strips. It was also observed that the active confinement of concrete by post-tensioning the confining element results in stiffer pre-peak response of concrete specimens than the usual passive confinement.     

An integrated thin-walled steel skeleton structure (two full scale tests)

The increased popularity of cold-formed thin-walled steel sections in housing construction has lead to an increased interest in the development of thin-walled frame buildings in accordance with seismic requirements. This paper investigates appropriate details for the main frame elements of a thin-walled building structure. Some of the proposed details are tested by two full scale one-storey frames under gravity and lateral cyclic loads. The results show that this type of structure offers a good potential for earthquake resistant construction, but more thorough studies are needed.     

Topology optimization for the seismic design of truss-like structures

A practical optimization method is applied to design nonlinear truss-like structures subjected to seismic excitation. To achieve minimum weight design, inefficient material is gradually shifted from strong parts to weak parts of a structure until a state of uniform deformation prevails. By considering different truss structures, effects of seismic excitation, target ductility and buckling of the compression members on optimum topology are investigated. It is shown that the proposed method could lead to 60% less structural weight compared to optimization methods based on elastic behavior and equivalent static loads, and is efficient at controlling performance parameters under a design earthquake.     

冷弯型钢抗弯框架的延性研究

对地震作用下抗弯框架中冷弯型钢构件的选用进行研究。冷弯型钢构件的主要不足是薄壁单元的平面外刚度很小,延性也很差。抗弯框架的主要构件为梁、柱及梁柱节点。在抗震框架中,梁能提供足够的延性,而其他单元主要受弹性域的限制。研究了带弯曲翼缘的新型冷弯型钢梁性能,并与传统钢梁比较。新型梁柱节点包含一个节点板,它能限制节点传递来的力引起的平面外变形。通过有限元分析,研究了新型冷弯型钢梁及梁柱节点的性能。结果表明:新型梁构件及节点的延性比传统冷弯型钢框架单元更好。     

Ancient road transport devices: Developments from the Bronze Age to the Roman Empire

The development of transportation systems has significantly enhanced the welfare and modernization of society. Wooden vehicles pulled by animals have been used for land transportation since the early Bronze Age. Whole-body gharries with rigid wheels pulled by oxen appeared in Crete by 2000 BC or earlier. Horses originating from the East were depicted in early Cretan seal-rings of the same period. The two-wheeled horsedrawn chariot was one of the most important inventions in history. This vehicle provided humanity its first concept of personal transport and was the key technology of war for 2000 years. Chariots of Mycenaean and Archaic Greece with light and flexible four-spoked wheels acting as spring suspensions were depicted in vase paintings. The development of this vehicle incorporated the seeds of a primitive design activity and was important for engineering. The Trojan horse since 1194 BC and the helepolis since 700 BC were the first known machines on a wheeled base transported by horses or self-powered. Ancient engineers invented bearings lubricated with fat, and Romans introduced the ancestors of ball bearings for their wagons and carts. The historic evolution of wheeled transportation systems, along with early traction, suspension, and braking systems, is presented in this paper. Analytical and numerical methods are incorporated to analyze the most conceivable loading situations of typically reconstructed wheeled transportation systems in ancient times. Traction requirements both for horse-driven machines and the power for internal motors are also analyzed. This study can serve as a basis for further development of detailed reconstruction of transportation systems in antiquity.     

Punching Shear Behavior of Fiber Reinforced Polymers Reinforced Concrete Flat Slabs: Experimental Study

This paper presents the results of a two-phase experimental program investigating the punching shear behavior of fiber reinforced polymer reinforced concrete (FRP RC) flat slabs with and without carbon fiber reinforced polymer (CFRP) shear reinforcement. In the first phase, problems of bond slip and crack localization were identified. Decreasing the flexural bar spacing in the second phase successfully eliminated those problems and resulted in punching shear failure of the slabs. However, CFRP shear reinforcement was found to be inefficient in enhancing significantly the slab capacity due to its brittleness. A model, which accurately predicts the punching shear capacity of FRP RC slabs without shear reinforcement, is proposed and verified. For slabs with FRP shear reinforcement, it is proposed that the concrete shear resistance is reduced, but a strain limit of 0.0045 is recommended as maximum strain for the reinforcement. Comparisons of the slab capacities with ACI 318-95, ACI 440-98, and BS 8110 punching shear code equations, modified to incorporate FRP reinforcement, show either overestimated or conservative results.     

Bond Behavior of Fiber Reinforced Polymer Bars under Direct Pullout Conditions

This paper examines the behavior of Eurocrete fiber-reinforced polymer (FRP) bars (glass, carbon, aramid, and hybrid) in concrete under direct pullout conditions. More than 130 cube specimens were tested in direct pullout where no splitting was allowed to develop. In normal concrete, the mode of bond failure of FRP bars was found to differ substantially from that of deformed steel bars because of damage to the resin rich surface of the bar when pullout takes place. Bond strengths developed by carbon fiber-reinforced polymer and glass fiber-reinforced polymer bars appear to be very similar and just below what is expected from deformed steel bars under similar experimental conditions. The load slip curves highlight some of the fundamental differences between steel and FRP materials. This paper reports in detail on the influence of various parameters that affect bond strength and development such as the embedment length, type, shape, surface characteristics, and diameter of the bar as well as concrete strength. The testing arrangement is also shown to influence bond strength because of the “wedging effect” of the bars.