Experimental study of the destruction in CFRP laminates at the macro-level by acoustic emission method

The author conducted experiments using the method of acoustic emission under uniaxial tension of specimens of CFRP laminates with different stacking, geometry and stress concentration. The influence of a mutual arrangement of the material destruction zone and the extensometer installation site on the nonlinear deformation is revealed. It is shown that the damage accumulation process is highly informative when determining the energy of AE pulses. The possibility of visualizing the formation and development of destruction zones in orthogonal directions, as well as the possibility of determining the moment of crack start from the apex of the notch during splitting, is established. The mechanism of alternating stress relaxation in two developed zones of destruction is revealed. The paper shows a high degree of correlation between mechanic and acoustic-emission events. Finally, the author suggests assessing the mechanical state of material with the account of obtained damages by the degree of its integrity (one to zero) depending on the load history, its individual geometric features and stress concentration.

Relationship Between Intrinsic Threshold Stress Intensity And Near-Tip Residual Stress: A Reference Material Property

The relationship between intrinsic, closure-free threshold stress intensity and near-tip residual stress, characterizes the effect of load magnitude as well as load history on near-threshold fatigue crack growth rates. It serves as a reference against which precise closure data can be extracted from growth rates to calibrate analytical estimates. These possibilities were subjected to rigorous experimental verification involving threshold and near-threshold fatigue response under overloads, underloads with load-shedding on a steel prone to oxide debris formation. The study reveals why conventional load shedding practice to characterize threshold stress intensity is prone to yield unconservative and misleading results.

Strengthening full-scale damaged prestressed concrete bridge girders with CFRP sheets

A large percentage of bridges in Canada were constructed over thirty years ago and their condition steadily declining. A product of deterioration and corrosive environments, many structures have been rendered unfit as per design codes and [are] structurally unsound. Constructing new structures and conventional repair methods are financially costly. A solution lies in fibre reinforced polymers (FRP). This thesis summarizes experimental projects regarding FRP usage in field applications. An actual damaged bridge girder was removed and rehabilitated with the FRP system. It was loaded incrementally and statically, nearing failure, investigating the reliability of the rehabilitation technique proposed to revive strength capacity to an acceptable level. A finite element computer simulation was created, modeling the load-history of the rehabilitated girder, as well as three full-scale damaged duble-tee girders, recently rehabilitated and loaded to collapse. This full-scale testing program and computer replication shall provide engineers with confidence in using FRP technology in girder strengthening.

Experimental study on web crippling of lapped cold-formed steel channels subjected to interior two-flange loading

The current North American Specifications for the Design of Cold-Formed Steel (CFS) Structural Members, AISI-S136-01, specifies expressions for web crippling strength of different joist geometries in case of exterior end and concentrated load locations. However, it does not permit an in increase two-flange loading. Thus, the objective of this research in this thesis is to generate experimental data for CFS channels where both webs of channel members are lapped at the interior support location and being loaded simultaneously. This thesis summarizes the results of a parametric study to examine few parameters that affect web crippling strength of such lapped channels. These parameters include the unbraced length of channel member, the presence screws, the level of flange restraint at the interior support location, channel six and load bearing length (i.e. lap length). Test specimens were loaded to failure and load history and the failure pattern were recorded. Based on experimental findings, a reliable and economical design expression was developed for web crippling strength of lapped CFS channels at interior support location when subjected to two-flange loading.

Experimental study on web crippling of lapped cold-formed steel channels subjected to interior two-flange loading

The current North American Specifications for the Design of Cold-Formed Steel (CFS) Structural Members, AISI-S136-01, specifies expressions for web crippling strength of different joist geometries in case of exterior end and concentrated load locations. However, it does not permit an in increase two-flange loading. Thus, the objective of this research in this thesis is to generate experimental data for CFS channels where both webs of channel members are lapped at the interior support location and being loaded simultaneously. This thesis summarizes the results of a parametric study to examine few parameters that affect web crippling strength of such lapped channels. These parameters include the unbraced length of channel member, the presence screws, the level of flange restraint at the interior support location, channel six and load bearing length (i.e. lap length). Test specimens were loaded to failure and load history and the failure pattern were recorded. Based on experimental findings, a reliable and economical design expression was developed for web crippling strength of lapped CFS channels at interior support location when subjected to two-flange loading.

Strengthening full-scale damaged prestressed concrete bridge girders with CFRP sheets

A large percentage of bridges in Canada were constructed over thirty years ago and their condition steadily declining. A product of deterioration and corrosive environments, many structures have been rendered unfit as per design codes and [are] structurally unsound. Constructing new structures and conventional repair methods are financially costly. A solution lies in fibre reinforced polymers (FRP). This thesis summarizes experimental projects regarding FRP usage in field applications. An actual damaged bridge girder was removed and rehabilitated with the FRP system. It was loaded incrementally and statically, nearing failure, investigating the reliability of the rehabilitation technique proposed to revive strength capacity to an acceptable level. A finite element computer simulation was created, modeling the load-history of the rehabilitated girder, as well as three full-scale damaged duble-tee girders, recently rehabilitated and loaded to collapse. This full-scale testing program and computer replication shall provide engineers with confidence in using FRP technology in girder strengthening.

Assessment of the Deterioration State of Post-Installed Bonded Anchors Using Ultrasonic

The assessment of already installed anchorages for a possible exceeding of the service load level is a question that is gaining more and more importance, especially in building maintenance. Bonded anchors are of particular interest here, as the detection of a capacity reduction or load exceedance can cause damage to the concrete-bonded mortar behavior. This article investigates the extent to which ultrasonic methods can be used to make a prediction about the condition of anchorages in concrete and about their load history. A promising innovative assessment method has been developed. The challenges in carrying out the experimental investigations are the arrangement of the transducers, the design of the test set-up and the applicability of direct, indirect or semidirect ultrasonic transmission. The experimental investigations carried out on a test concrete mix and a bonded anchor system show that damage to the concrete structure can be detected by means of ultrasound. The results indicate the formation of cracks and therefore a weakening of the response determined by means of direct, indirect and semidirect ultrasonic transmission. However, for application under non-laboratory conditions and on anchors with unknown load history, the calibration with a reference anchor and the identification of the maximum load is required. This enables a referencing of the other loaded anchors to the unloaded conditions and allows an estimation of the load history of individual anchors.