Improving the Long-term Performance of Full-depth Precast Concrete (FDPC) Deck Panels Using Non-Proprietary UHPC

Full-depth precast concrete (FDPC) deck panels are a type of prefabricated bridge element used in accelerated bridge construction (ABC) that have been used in bridge construction since the 1960’s as an alternative to conventional CIP decks. The main purpose of using the prefabricated elements is to accelerate the construction and increase the long-term performance. FDPC deck panels itself offers superior durability and performance, but the connection between these elements still have shown some long-term issues like cracking. Ultra-high-performance concrete (UHPC) is an innovative and commercially available material that has been used to address concerns related to connection between precast elements. The high compressive strength and tensile strength alongside with superior durability of UHPC, has made it a solution for addressing the performance issue related to connection precast members, but its relatively high cost, has limited its widespread use. Hence, the non-proprietary UHPC was considered as an alternative of commercial UHPC with significantly lower price. In this study, previous investigations on FDPC deck panels were reviewed and a database for bridges constructed with FDPC deck panels were created and their long-term performance were predicted and compared with bridges constructed with cast in place deck. Then, a comprehensive experimental work was conducted to develop the non-proprietary UHPC using locally available material. This research was expanded numerically then by studying the performance of non-proprietary UHPC in joint between FDPC deck panels. Finite element numerical analysis using ATENA was performed to compare the performance of developed non-proprietary UHPC with commercial UHPC in joint applications. Six different numerical specimens with different joint width were considered and the performance of different material under static loading were analyzed. Results, revealed that the developed non-proprietary UHPC in this study, can perform similar to specimens with commercial UHPC joints. As it was expected, sensitivity analysis determined that tensile strength, tension function of UHPC and its bond behavior with precast elements, play the critical role and having a very high compressive strength and modulus of elasticity is not a big advantage when it is used to connect precast members under flexural load

Net Section Fracture Assessment of Welded Rectangular Hollow Structural Sections

Rectangular Hollow Sections (RHS) because of their high resistance to tension, as well as compression, are commonly used as a bracing member with slotted gusset plate connections in steel structures. Since in this type of connection only part of the section contributes in transferring the tensile load to the gusset plate, shear lag failure may occur in the connection. The AISC specification decreases the effective section net area by a factor to consider the effect of shear lag for a limited connection configuration. This study investigates the effective parameters on the shear lag phenomenon for rectangular hollow section members connected at corners using a single concentric gusset plate. The results of the numerical analysis show that the connection length and connection eccentricity are the only effective parameters in the shear lag, and the effect of gusset plate thickness is negligible because of the symmetric connection. The ultimate tensile capacity of the suggested connection in this study were compared to the typical RHS connection presented in the AISC and the similar double angle sections connected at both legs. The comparison indicates that tensile performance of the suggested connection in this study because of its lower connection eccentricity is much higher than the typical slotted connection and double angle connections. Therefore, a new equation is suggested based on the finite element analyses to modify the AISC equation for these connections

Improvement of Concrete Characterization Using Nanosilica

In recent years, different research works have been conducted to evaluate the addition of nanometer materials to concrete materials. In this paper, the influence of Nanosilica on compressive strength, abrasive strength, durability, and improvements in the micro-structure of concrete are discussed. The results showed that the compressive strength of concrete samples with Nanosilica and silica fume were higher than the compressive strength of other samples without nanometer materials in all ages, as well as increasing the dosage percentage of Nanosilica led to higher levels of compressive strength. In the mix designs with an equal dosage percentage, samples containing Nanosilica have shown a higher level of strength in comparison to samples containing silica fume. The application of Nanosilica in self-compacting concrete resulted in higher level of compressive strength, flexural strength, abrasive strength, elasticity module, ultrasonic waves permeability velocity (UPV), and lower water absorption compared to samples without Nanoparticles. Despite the evidences which show the improvement in mechanical characteristics of concretes with Nanosilica-particles, further developments for the applicability of Nanoparticles for improving the characteristics of concrete require the right knowledge and higher control over the effective mechanisms of Nanoparticles on concrete’s structure

Field studies on the effects of under sleeper pads in lateral resistance of railway

Under sleeper pads are used in several areas, specially, in places where transfer of vibrations to the surrounding areas should be limited. Beside of all advantages of this elements in the field of reducing costs of repair and maintenance of railway, improvement of line geometry, decreasing the thickness of required ballast, reduction of vibrations and disturbing noises coming from passing trains and increasing trip convenience, use of these pads according to thickness and hardness of them could be effective in lateral resistance. Based on international evaluations in the field of under sleeper pads, results of influence of under sleeper pads in lateral resistance  of railway are various, because of different reasons including: contact quality and compression of ballast grains, ballast thickness, distance between sleepers and different test for estimating the lateral resistance, therefore application of these pads specially in mountainous ways that lateral resistance is important, influence of these pads must be cleared. So in this field of study, lateral resistance of railway is measured by Single Tie Push Test. In this study 150 polyurethane under sleeper pads with two different stiffness which were produced by Getzner Company (specialize in vibration insulation in the rail), used in real line. Results of this field examinations show utilization of these elements under the sleepers increase 9.6% for the lateral resistance when SLB 3007 G (which are stiffer) attached in comparison to sleepers without pad and 2.54%  decrease when SLB 1308 G attached in comparison to sleepers without pad. However decrease in hardness, results in increasing rate of lateral resistance reduction