Nasim Uddin

Structural Characterization of Hybrid Fiber Reinforced Polymer (FRP)-Autoclave Aerated Concrete (AAC) Panels

The structural characterization of hybrid fiber reinforced polymer (FRP)-autoclaved aerated concrete (AAC) panels is examined in this study. The structural system is based on the concept of a sandwich construction with strong and stiff FRP composite skins bonded to an inner AAC panel. The FRP composite material is made of carbon reinforcing fabrics embedded in an epoxy resin matrix. The carbon fiber reinforced polymer (CFRP) reinforcement is applied on the top and bottom faces of the AAC panel, and several innovative processing techniques are used including the hand lay-up as well as the vacuum assisted resin transfer molding (VARTM). The main focus of the research is to combine the AAC with the FRP face sheets into a synergetic system, which would be consistent with the recent interest in high performance and zero maintenance of civil infrastructures. This combination, being lightweight in nature, has the potential to be used for speedy panelized construction purposes, for disaster mitigation, and to prevent labor-intensive construction. The CFRP has been used with regular concrete before and has shown phenomenal reinforcing capabilities. The AAC, on the other hand, is a cellular concrete and is very light to work with, in comparison to normal concrete. It is also structurally very brittle in nature and has much lower flexural as well as compressive strengths than normal weight concrete. An experimental protocol based on a four point bending test is used to characterize the stiffness, ductility, and strength response of the hybrid FRP-AAC sandwich panels. Since there are no previous research data available on the hybrid CFRP-AAC panels and the bonding characteristics of AAC with FRP are unknown, a set of basic tests are also initiated including the bonding test on AAC samples wrapped with CFRP. To understand and optimize the flexural/shear behavior of the hybrid CFRP-AAC sandwich panels, several innovative reinforcing schemes with CFRP skin are used, as elaborated in this article. In addition, both continuous and discrete AAC blocks are used to fabricate AAC panels. Results from the experiments emphasize the need for a complementary test program where the best reinforcing scheme from the study would be duplicated in future tests on structural elements of the typical sizes including beams, floors, lintels, etc.

Identification of Vehicular Axle Weights with a Bridge Weigh-in-Motion System Considering Transverse Distribution of Wheel Loads

A modified two-dimensional (2D) Moses algorithm for acquiring the field-calibrated influence line (IL) of an existing bridge is presented, based on strain data acquired continuously at a high scanning rate with calibration vehicles of known axle weights and axle spacings crossing an instrumented bridge. Considering the transverse distribution of the wheel loads on each girder attributable to the 2D behavior of the slab-girder bridge, the IL of each of the girders can be calculated, which does not require the girders to possess identical material and geometric properties. By using the calculated IL of each girder as a reference, a modified 2D Moses algorithm was derived to identify axle weights of moving vehicles, taking into consideration the transverse distribution of the wheel loads on each girder. Mathematical equations to calculate ILs and axle weights were derived, and the proposed algorithms were implemented by a computer program. The accuracy of the IL calculation and axle weight identification was verified through a field test of a bridge on U.S. Route 78 in Alabama. The identified axle weights showed agreement with the static measurements from weighing pads and with results from the bending-plate weigh-in-motion (BPWIM) system near the instrumented bridge.

Flexural Behavior of Full-Scale Composite Structural Insulated Floor Panels

Panelized systems are prefabricated components that are brought to a construction site and assembled into the finished structure. Traditional constructions are often subjected to termite attack, mold buildups and have poor penetration resistance against wind-borne debris. To overcome these problems, a new type of composite structural insulated panel (CSIP) was developed and is analyzed in this study for structural floor applications. The concept of the panel is based on the theory of sandwich construction. The proposed composite panel is made of low cost orthotropic thermoplastic glass/polypropylene (glass–PP) laminate as a facesheet and expanded polystyrene foam (EPS) as a core. Full scale experimental testing was conducted to study the flexural behavior of the CSIP floor member. CSIP floor panels failed due to facesheet/core debonding. Analytical modeling was further presented to predict the interfacial tensile stress at the core/facesheet interface, critical wrinkling stress, flexural strength and deflections for structural CSIP floor panels. The experimental results were validated using the proposed models and were in good agreement.

Structural Behavior of Fiber-Reinforced Polymer-Autoclaved Aerated Concrete Panels

Autoclaved aerated concrete (AAC) is an ultra-lightweight concrete with 1/5 the weight of ordinary concrete due to entrained air bubbles. This paper examines the structural behavior of carbon fiber-reinforced polymer (CFRP)-AAC panels, with the ultimate goal of contributing to tools for the design of CFRP-AAC panels for building construction. The structural system is based on the concept of sandwich construction with strong and stiff FRP composite skins bonded to an inner AAC panel. The CFRP reinforcement was applied on the top and bottom faces of the AAC panel using several processing techniques, including hand lay-up as well as vacuum-assisted resin transfer molding. Several reinforcing schemes with the CFRP skin were used to optimize flexural/shear behavior of the hybrid CFRP-AAC sandwich panels. Experimental results showed that the AAC beams demonstrated an increase in ultimate flexural capacity and stiffness due to the influence of the FRP. Most of the CFRP-AAC panels remained intact even after the ultimate load had been reached. The load-deflection curves showed a ductile behavior of the panels that indicates that the CFRP-AAC combination is synergetic in nature. Overall, AAC bonds well with the CFRP provided that the processing, compaction and curing are done properly.

Geotechnical Issues in the Creation of Underground Reservoirs for Massive Energy Storage

The primary objective of this paper is to present and discuss geotechnical issues and challenges for the design and stability of massive energy storage caverns in hard rock formations. In general, the challenges which confront the construction of massive underground caverns are a combination of the geological, hydrological, geochemical, geothermal, and geotechnical. The identification and remediation of the geotechnical challenges will be qualitatively discussed here and this discussion will be anchored with a particular practical example.

Manufacturing and Structural Feasibility of Natural Fiber Reinforced Polymeric Structural Insulated Panels for Panelized Construction

Natural fibers are emerging in the fields of automobile and aerospace industries to replace the parts such as body panels, seats, and other parts subjected to higher bending strength. In the construction industries, they have the potential to replace the wood and oriented strand boards (OSB) laminates in the structural insulated panels (SIPs). They possess numerous advantages over traditional OSB SIPs such as being environmental friendly, recyclable, energy efficient, inherently flood resistant, and having higher strength and wind resistance. This paper mainly focuses on the manufacturing feasibility and structural characterization of natural fiber reinforced structural insulated panels (NSIPs) using natural fiber reinforced polymeric (NFRP) laminates as skin. To account for the use of natural fibers, the pretreatments are required on natural fibers prior to use in NFRP laminates, and, to address this issue properly, the natural fibers were given bleaching pretreatments. To this end, flexure test and low-velocity impact (LVI) tests were carried out on NSIPs in order to evaluate the response of NSIPs under sudden impact loading and uniform bending conditions typical of residential construction. The paper also includes a comparison of mechanical properties of NSIPs with OSB SIPs and G/PP SIPs. The results showed significant increase in the mechanical properties of resulting NSIP panels mainly a 53% increase in load-carrying capacity compared to OSB SIPs. The bending modulus of NSIPs is 190% higher than OSB SIPs and 70% weight reduction compared to OSB SIPs.

Debonding of composites structural insulated sandwich panels

A new type of composites structural insulated panels (CSIPs) is presented in this article. These panels are proposed for structural floor and wall applications. The developed composite panels are made of low-cost orthotropic thermoplastic glass/polypropylene laminate as facesheets and expanded polystyrene foam as a core. CSIPs have a considerably high facesheet/core moduli ratio. The common mode of failure of these panels is facesheet/core debonding. Accordingly, this investigation presents models for interfacial tensile stress and critical wrinkling in-plane stress associated with debonding of CSIPs. The facesheet in compression was modeled as a beam on a Winkler foundation. The proposed models were validated using full-scale experimental testing for CSIPs floor and wall panels. Both type of panels failed by facesheet/ debonding with natural half-wavelength approximately equal to the core thickness.

Cost-effective bridge girder strengthening using vacuum-assisted resin transfer molding (VARTM)

The objective of this paper is to present the results of a demonstration project to apply externally bonded CFRP fabrics to retrofit a simple span prestressed concrete girder with improved repair and hardening techniques. The technique, Vacuum Assisted Resin Transfer Molding (VARTM), newly introduced to civil infrastructure was implemented in the field within two days without any traffic interruption. As an alternative to traditional hand lay up, VARTM has several processing advantages, like saving the processing time, uniform resin application, intimate contact between each layer of CFRP and concrete substrate ensuring good consolidation to remove void or dry spot, higher fiber volume fraction (about 70%) and greater wettability of the fiber, etc. The performance of the strengthened structures depends on the above potential factors to obtain high structural performance. VARTM uses single-sided molding technology to infuse resin over fabrics wrapping large structures such as bridge girders and saving tooling and processing time. Recently, the VARTM technique has been implemented in strengthening of an I-565 highway bridge girder in Huntsville, Alabama. Laboratory investigation included the construction of small concrete prisms to study the bonding behavior of Carbon Fiber Reinforced Polymer (CFRP) and strengthened concrete beams using VARTM to simulate the performance with and without strengthening. To the end, the process of field demonstration of this newly introduced technique to civil infrastructure has been presented.

Structural Characterization of Natural Fiber Reinforced Polymeric (NFRP) Laminates for Building Construction

This study focuses on the structural characterization of Natural Fiber Reinforced Polymeric (NFRP) laminates for their potential application in structural insulated panels in order to replace traditional Oriented Strand Board (OSB) laminates. To this end, mechanical testing such as bending test and low velocity impact test were performed on the laminates made up of bleached and unbleached jute fibers and the results were compared with OSB laminates and Glass/Polypropylene (G/PP) laminates. The results showed significant improvement in the mechanical properties of the resulting laminates such as bending strength by 176%, the modulus of elasticity by 129% and, the load carrying capacity by 179%. The energy absorbed by NFRP was 18% higher than OSB and 26% higher resistance to impact loading.

Bond Strength of Carbon Fiber Sheet on Concrete Substrate Processed by Vacuum Assisted Resin Transfer Molding

High quality and expedient processing repair methods are necessary to enhance the service life of bridge structures. Deterioration of concrete can occur as a result of structural cracks, corrosion of reinforcement, and freeze–thaw cycles. Cost effective methods with potential for field implementation are necessary to address the issue of the vulnerability of bridge structures and how to repair them. Most infrastructure related applications of fiber-reinforced plastics (FRPs) use traditional hand lay-up technology. The hand lay-up is tedious, labor-intensive and relies upon personnel skill level. An alternative to traditional hand lay-up of FRP for infrastructure applications is Vacuum Assisted Resin Transfer Molding (VARTM). VARTM uses single sided molding technology to infuse resin over fabrics wrapping large structures, such as bridge girders and columns. There is no work currently available in understanding the interface developed, when VARTM processing is adopted to wrap fibers such as carbon and/or glass over concrete structures. This paper investigates the interface formed by carbon fiber processed on to a concrete surface using the VARTM technique. Various surface treatments, including sandblasting, were performed to study the pull-off tensile test to find a potential prepared surface. A single-lap shear test was used to study the bond strength of CFRP fabric/epoxy composite adhered to concrete. Carbon fiber wraps incorporating Sikadur HEX 103C and low viscosity epoxy resin Sikadur 300 were considered in VARTM processing of concrete specimens.