Shear-flexural cracking strength of RC beams with external vertical prestressing rebars: Theoretical investigation and numerical simulation

This paper presents a semi-theoretical empirical formula to predict the shear-flexural cracking strength of an RC beam enhanced with the external vertical prestressing rebar (EVPR) technique. Besides, nonlinear finite element models (FEM) created by software ABAQUS were used to analyze the effect of crucial parameters on the shear-flexural cracking strength. The parameters involve shear span-to-depth ratio, concrete strength, longitudinal tension reinforcement ratio, initial pulling force and spacing of EVPRs, and the vertical stiffness of the EVPR supports. Results show that the cracking strength increased linearly with the tensile strength of the concrete and the initial pulling force. The small shear span-to-depth ratio was predominantly conducive to the cracking strength. Adequate longitudinal tension rebars contributed to the cracking strength improvement. A reasonable EVPR spacing was recommended to ensure the cracking strength. Greater vertical stiffness of the EVPR supports can ensure higher compressive stress for the RC beam to improve the cracking strength.

A Study of 100 tonf Tensile Load for SMART Mooring Line Monitoring System Considering Polymer Fiber Creep Characteristics

Mooring systems are among the most important elements employed to control the motion of floating offshore structures on the sea. Considering the use of polymer material, a new method is proposed to address the creep characteristics rather than the method of using a tension load cell for measuring the tension of the mooring line. This study uses a synthetic mooring rope made from a polymer material, which usually consists of three parts: center, eye, and splice, and which makes a joint for two successive ropes. We integrate the optical sensor into the synthetic mooring ropes to measure the rope tension. The different structure of the mooring line in the longitudinal direction can be used to measure the loads with the entire mooring configuration in series, which can be defined as SMART (Smart Mooring and Riser Truncation) mooring. To determine the characteristics of the basic SMART mooring, a SMART mooring with a diameter of 3 mm made of three different polymer materials is observed to change the wavelength that responds as the length changes. By performing the longitudinal tension experiment using three different SMART moorings, it was confirmed that there were linear wavelength changes in the response characteristics of the 3-mm-diameter SMART moorings. A 54-mm-diameter SMART mooring is produced to measure the response of longitudinal tension on the center, eye, and splice of the mooring, and a longitudinal tension of 100 t in step-by-step applied for the Maintained Test and Fatigue Cycle Test is conducted. By performing a longitudinal tension experiment, wavelength changes were detected in the center, eye, and splice position of the SMART moorings. The results obtained from each part of the installed sensors indicated a different strain measurement depending on the position of the SMART moorings. The variation of the strain measurement with the position was more than twice the result of the difference measurement, while the applied external load increased step-by-step. It appears that there is a correlation with an externally generated longitudinal tensional force depending on the cross-sectional area of each part of the SMART mooring.

Fine adaptive control of precision grip without maximum pinch strength changes after median nerve mobilization

ABSTRACTFine dexterity critically depends on information conveyed by the median nerve. While the effects of its compression and vibration are well characterized, little is known about longitudinal tension and excursion. Using a force-sensitive manipulandum, a numeric dynamometer and Semmes-Weinstein monofilaments, we examined the adaptations of precision grip control, maximum pinch strength and fingertips pressure sensation threshold before and immediately after the application of longitudinal tension and excursion mobilizations applied on the median nerve. Grip (GF) and load (LF) forces applied by the thumb, index and major fingers were collected in 40 healthy young participants during three different grip precision tasks along the direction of gravity. For grip-lift-drop task, maximum GF and LF and their first time derivatives were computed. For up-down oscillations, means of GF and LF and their variability were computed. For oscillations with up and down collisions, peaks of GF and LF, time delay between GF peak and contact, and values of GF and LF at contact were collected. Our findings show that median nerve mobilizations induce significant fine adaptations of precision grip control in the three different tasks but mainly during grip-lift-drop and oscillations with collisions. Fingertips pressure sensation thresholds at index and thumb were significantly reduced after the mobilizations. No significant changes were observed for maximum pinch strength. We conclude that precision grip adaptations observed after median mobilizations could be partly explained by changes in cutaneous median-nerve mechanoreceptive afferents from the thumb and index fingertips.

REDUCTION IN HAMSTRING AUTOGRAFT DIAMETER AS A RESULT OF ACL RECONSTRUCTION PREPARATION USING LONGITUDINAL TENSION AND CIRCUMFERENTIAL COMPRESSION

Background: Previous studies have investigated the effect of tension and circumferential compression on the diameter of fresh-frozen anterior cruciate ligament (ACL) allografts, but no study has described the effect on soft tissue ACL autografts harvested for implantation in the operating room for ACL reconstruction. The purpose of this study was to elucidate how hamstring autograft diameter changes during preparation for ACL reconstruction with compression in addition to tensioning. We hypothesized that autograft diameter would decrease as the graft was prepared with both tension and circumferential compression. Operative complications related to graft compression were also investigated. Methods: 100 ACL reconstruction surgeries (Age M = 15.3 ± 2.2 years; 53% male) were identified among two orthopedic surgeons. Hamstring tendon grafts were prepared in a standardized procedure to produce a looped graft for all-inside ACL reconstruction. Autografts were tensioned to 15-20 lbs and then their tibial and femoral diameters were measured using cylindrical sizing blocks. The graft diameters were measured again after placement under a saline soaked gauze for 10 minutes with the sizing blocks in place. A Wilcoxon signed rank test with correction for continuity was performed to detect significant change in autograft diameters after compression. Results: Treatment of hamstring autografts with longitudinal tension and circumferential compression significantly decreased the median tibial and femoral graft diameters by 0.75 mm. The median tibial diameter decreased from 9.50 mm to 8.75 mm (p < 0.0001) and the median femoral diameter decreased from 9.50 mm to 8.50 mm (p < 0.0001). 72% of all autografts had the same tibial and femoral diameters at implant. No intraoperative complications were noted with implantation of compressed grafts in smaller diameter tunnels. Conclusions: Median diameters of ACL hamstring autografts harvested in the OR decreased by 0.75 mm after treatment with circumferential compression using cylindrical sizing blocks. This decreased the socket size by one to two 0.5 mm sizes with no adverse events noted intra-operatively due to the compression of the grafts or the smaller sockets. Clinical Relevance: Graft integration in a bone tunnel is dependent on optimal fit of the graft inside the tunnel. If the tunnel is too small, the graft will not fit and if it is too large, it may allow joint fluid into the tunnel leading to tunnel widening and incomplete integration. Pre-tensioning a graft has been noted for many years to be an important way to properly establish the length-tension relationship of a graft. Here, we show that circumferential compression of the graft prior to implantation significantly changes the size of the graft, and thus the size of the tunnels required for implantation. In addition to providing better graft tunnel match, using smaller tunnels requires less bone removal which is particularly advantageous for pediatric, revision, and double bundle ACL reconstruction techniques where space for tunnel drilling is limited.