Effect of vertical prestressing on the punching failure

The phenomenon of the punching failure of circular reinforced concrete slabs, and the effect of the vertical prestressing on the failure mechanism has been investigated in this paper. The phenomenon was investigated using a finite element package and results were compared with existing experimental data. Results show that slab's ultimate behavior is governed by material behavior within the compressive force path. Vertical prestressing improves triaxial compressive stress state of the critical zone within the compressive force path, and thus results in significantly increased ultimate load and ductility of the slab.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31053/1/0000730.pd

Acoustic Inspection of Coated Steel Bar in Reinforced Concrete Structure

Bridges with reinforcement corrosion problems are now under careful inspection in Taiwan. Costly maintenance programs are underway and raising serious safety concern. There are various engineering solutions to salt-induced corrosion. Among them epoxy-coated reinforcing bars, commonly referred to as rebar, are frequently used in marine environment and other areas due to its durability, reasonable cost, and convenience. However, coated rebar has lower bond strength and is less ductile than uncoated rebar. Thus it could result in larger crack width during pull-out tests [1,2]. The bond strength between coated steel bars and covered concrete results from the adhesion at the steel-concrete boundary, the factional force, and the interlocking force provided by the raised ribs at the steel bar surface. The interlocking force is much stronger than the other two, while the factional force occurs only if the adhesion vanishes after delamination or disbonding starts

Effect of increased tensile strength and toughness on reinforcing-bar bond behavior

The research reported here investigated the pull-out behavior of deformed reinforcing bars embedded in fiber-reinforced-concrete (FRC) and high-performance- fiber-reinforced-concrete (HPFRC) matrices exhibiting increased tensile strength and toughness. Increased strength and toughness of the embedding matrix resulted in a significant increase in pull-out strength, strain capacity, and over-all ductility, as well as more stable crack development. Additionally, when sufficient lateral constraint (i.e. cover thickness) was provided, the use of an HPFRC matrix exhibiting strain-hardening behavior resulted in a slip-hardening pull-out response.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31895/1/0000848.pd

On the fatigue response of a bonded repaired aerospace composite using thermography

Lock-in thermography was employed to investigate the repair efficiency of a bonded repaired aerospace composite subjected to step-wise cycling mechanical loading. The studied component (substrate) was artificially damaged with a 5 mm circular notch and subsequently repaired with a tapered bonded patch. Critical and sub-critical damage of the repaired component was monitored via thermography during 5 Hz tension–tension fatigue. The examination of the acquired thermographs enabled the identification of the patch debonding propagation as well as the quantification of the stress magnification at the patch ends and the locus of the circular notch. It was found that fatigue mechanical loading yields both thermoelastic and hysterestic phenomena with the latter being more prominent prior to the failure of the studied repaired component

A Critical Review on the Structural Health Monitoring Methods of the Composite Wind Turbine Blades

With increasing turbine size, monitoring of blades becomes increasingly im-portant, in order to prevent catastrophic damages and unnecessary mainte-nance, minimize the downtime and labor cost and improving the safety is-sues and reliability. The present work provides a review and classification of various structural health monitoring (SHM) methods as strain measurement utilizing optical fiber sensors and Fiber Bragg Gratings (FBG’s), active/ pas-sive acoustic emission method, vibration‒based method, thermal imaging method and ultrasonic methods, based on the recent investigations and prom-ising novel techniques. Since accuracy, comprehensiveness and cost-effectiveness are the fundamental parameters in selecting the SHM method, a systematically summarized investigation encompassing methods capabilities/ limitations and sensors types, is needed. Furthermore, the damages which are included in the present work are fiber breakage, matrix cracking, delamina-tion, fiber debonding, crack opening at leading/ trailing edge and ice accre-tion. Taking into account the types of the sensors relevant to different SHM methods, the advantages/ capabilities and disadvantages/ limitations of repre-sented methods are nominated and analyzed

Experimental Testing of Single APM Spheres

Advanced pore morphology (APM) foam, consisting of sphere-like metallic foam elements, proves to have advantageous mechanical properties and unique application adjustability. Since the APM foam manufacturing procedure has been developed recently, the mechanical characterization of these materials is still very limited. Therefore, the purpose of this research was to determine the behaviour of APM spheres and its composites when subjected to quasi-static and dynamic compressive loading. The results of the performed research have shown valuable mechanical properties of the composite APM foam structures, offering new possibilities for their use in general engineering applications

The detection of plastic flow propagation based on the temperature gradient

Heat generation during the dynamic loading and plastic flow process in material is the basic of theory of plasticity. The infrared thermography based on the middle wave camera provides tracking the thermal phenomena in material associated with the plastic flow during the dynamic loads process. The temperature gradient has been applied to track the heat propagation direction and consequently plastic flow in materials and structures. Closed cell aluminum metal foam, foamed within a structural member, is evaluated as an energy absorber. The thermographic approach enabled to trace and evaluate energy absorption performances of hollow structural members with metal foam filler material.publishe