Assessment of Concrete Filled Steel Tubular Members: An Experimental Review

In this world with rapid development, durable and fast construction techniques lead to the invention of composite materials that are robust and advantageous over conventional materials. Recently invented Concrete-filled steel tubular members are the composite members used in civil engineering works to replace conventional steel and concrete members. This paper deals with an overview of the experimental performance of various types of composite members such as columns, short columns, stub columns, beam-columns, and slender columns deals with various loads such as axial compression, flexural load, cyclic bending, long-term sustained load, torsional load, and impact load. Effects due to the variation in the parameters like steel and concrete strength, diameter to thickness ratio, axial load level, shapes of tubes of these composite members on load-carrying capacity, flexural stiffness, ductility, torsional capacity, and cyclic performance of these members are discussed in this paper. The future scope is mentioned for study related to these composite members in the paper.

Sustained Loading Bond Response and Post-Sustained Loading Behaviour of NSM CFRP-Concrete Elements under Different Service Temperatures

Nowadays, one of the foremost procedures for strengthening concrete structures is the Near-Surface Mounted (NSM) technique. This paper presents an experimental study on the effect sustained loading and different service temperatures (steady and cyclic) have on NSM Carbon Fibre-Reinforced Polymer (CFRP)-concrete bonded joints and their post-sustained loading load-slip behaviour. Four experimental campaigns using eight NSM CFRP-concrete specimens were performed by employing two different service load levels (15% and 30% of the ultimate load) and combining two groove thicknesses (7.5 and 10 mm) and two bonded lengths (150 and 225 mm). Two steady state temperatures (20 and 40 °C) and two cyclic service temperatures (ranging between 20 and 40 °C) were programmed. The slip obtained was proportional to the sustained load level. Furthermore, higher slips were registered for specimens under higher mean temperatures in the cycle. After 1000 h of sustained load testing, the specimens were tested under monotonic loading until failure (post-sustained loading tests). In general, the ratio between the post-sustained loading ultimate load and the instantaneous ultimate load was close to the unity, although some differences were perceived in series S2 (steady 37.7 °C) with a mean increase of 6.3%, and series S3-B (cyclic temperature ranging between 24.6 and 39.2 °C) with a mean reduction of 9%.

Analysis of the Impact of Sustained Load and Temperature on the Performance of the Electromechanical Impedance Technique through Multilevel Machine Learning and FBG Sensors

The electro-mechanical impedance (EMI) technique has been applied successfully to detect minor damage in engineering structures including reinforced concrete (RC). However, in the presence of temperature variations, it can cause false alarms in structural health monitoring (SHM) applications. This paper has developed an innovative approach that integrates the EMI methodology with multilevel hierarchical machine learning techniques and the use of fiber Bragg grating (FBG) temperature and strain sensors to evaluate the mechanical performance of RC beams strengthened with near surface mounted (NSM)-fiber reinforced polymer (FRP) under sustained load and varied temperatures. This problem is a real challenge since the bond behavior at the concrete–FRP interface plays a key role in the performance of this type of structure, and additionally, its failure occurs in a brittle and sudden way. The method was validated in a specimen tested over a period of 1.5 years under different conditions of sustained load and temperature. The analysis of the experimental results in an especially complex problem with the proposed approach demonstrated its effectiveness as an SHM method in a combined EMI–FBG framework.

Effect of the Mechanical Load on the Carbonation of Concrete: A Review of the Underlying Mechanisms, Test Methods, and Results

As one of the major causes of concrete deterioration, the carbonation of concrete has been widely investigated over recent decades. In recent years, the effect of mechanical load on carbonation has started to attract more attention. The load-induced variations in crack pattern and pore structure have a significant influence on CO2 transport which determines the carbonation rate. With different types of load, the number, orientation, and position of the induced cracks can be different, which will lead to different carbonation patterns. In this review paper, the carbonation in cracked and stress-damaged concrete is discussed first. Then, literature about the effect of sustained load during carbonation is compared in terms of load type and load level. Finally, the advantages and disadvantages of possible test methods for investigating the effect of sustained load on carbonation are discussed with respect to loading devices, load compensation, and specimen size.

Mechanisms governing protective pregnancy-induced adaptions of the pelvic floor muscles in the rat pre-clinical model

Background: The intrinsic properties of pelvic soft tissues in women who do and do not sustain birth injuries are likely divergent, however little is known about this. Rat pelvic floor muscles undergo protective pregnancy-induced structural adaptations, sarcomerogenesis and increase in intramuscular collagen content, that protect against birth injury. Objectives: We aimed to test the following hypotheses: 1) increased mechanical load of gravid uterus drives antepartum adaptations; 2) load-induced changes are sufficient to protect pelvic muscles from birth injury. Study Design: Independent effects of load uncoupled from hormonal milieu of pregnancy were tested in 3- to 4-month-old Sprague-Dawley rats randomly divided into four groups, N=5-10/group: (1) load-/pregnancy hormones- (controls); (2) load+/pregnancy hormones-; (3) reduced load/pregnancy hormones+; (4) load+/pregnancy hormones+. Mechanical load simulating a gravid uterus was simulated by weighing uterine horns with beads similar to fetal rat size and weight. Reduced load was achieved by unilateral pregnancy after unilateral uterine horn ligation. To assess acute and chronic phases required for sarcomerogenesis, rats were sacrificed at 4 hours or 21 days post bead loading. Coccygeus, iliocaudalis, pubocaudalis and non-pelvic tibialis anterior were harvested for myofiber and sarcomere length measurements. Intramuscular collagen content was assessed using hydroxyproline assay. Additional 20 load+/pregnancy hormones- rats underwent vaginal distention to determine whether load-induced changes are sufficient to protect from mechanical muscle injury in response to parturition-associated strains of various magnitude. Data, compared using two-way repeated measures analysis of variance/pairwise comparisons, are presented as mean +/- standard error of mean. Results: Acute increase in load resulted in significant pelvic floor muscle stretch, accompanied by acute increase in sarcomere length compared to non-loaded control muscles (coccygeus: 2.69+/-0.03 vs 2.30+/-0.06 micrometers, P<0.001; pubocaudalis: 2.71+/-0.04 vs 2.25+/-0.03 micrometers, P<0.0001; iliocaudalis: 2.80+/-0.06 vs 2.35+/-0.04 micrometers, P<0.0001). After 21 days of sustained load, sarcomeres returned to operational length in all pelvic muscles (P>0.05). However, the myofibers remained significantly longer in load+/pregnancy hormones- compared to load-/pregnancy hormones- in coccygeus (13.33+/-0.94 vs 9.97+/-0.26 millimeters, P<0.0001) and pubocaudalis (21.20+/-0.52 vs 19.52+/-0.34 millimeters, P<0.04) and not different from load+/pregnancy hormones+ (12.82+/-0.30 and 22.53+/-0.32millimeters, respectively, P>0.1), indicating that sustained load induced sarcomerogenesis in these muscles. Intramuscular collagen content in load+/pregnancy hormones- group was significantly greater relative to controls in coccygeus (6.55+/-0.85 vs 3.11+/-0.47 micrograms/milligram, P<0.001) and pubocaudalis (5.93+/-0.79 vs 3.46+/-0.52 micrograms/milligram, P<0.05) and not different from load+/pregnancy hormones+ (7.45+/-0.65 and 6.05+/-0.62 micrograms/milligram, respectively, P>0.5). Iliocaudalis required both mechanical and endocrine cues for sarcomerogenesis. Tibialis anterior was not affected by mechanical or endocrine alterations. Despite equivalent extent of adaptations, load-induced changes were only partially protective against sarcomere hyperelongation. Conclusions: Load induces plasticity of the intrinsic pelvic floor muscle components that renders protection against mechanical birth injury. The protective effect, which varies between individual muscles and strain magnitudes, is further augmented by the presence of pregnancy hormones. Maximizing impact of mechanical load on pelvic floor muscles during pregnancy, such as with specialized pelvic floor muscle stretching regimens, is a potentially actionable target for augmenting pregnancy-induced adaptations to decrease birth injury in women who may otherwise have incomplete antepartum muscle adaptations.