Numerical Analysis of Microcracks of Fly Ash/Slag Concrete with Cobble as Coarse Aggregate

In order to improve mechanical properties of fly ash/slag concrete with large size cobble as coarse aggregate, this paper analyzes the effect of different factors on the concrete through the flexural strength test. The Monte Carlo simulation is used in the finite element solver of ANSYS to conduct the four-point bending beam test. Three-dimensional and two-dimensional finite element models are established to discuss how the gradation of large size cobbles affects the performance of the concrete by comparing macromechanical experiments. Results show that the gradation of large size cobbles is the main factor affecting the performance of the concrete. Slag generates the least effect on the concrete with cobble as coarse aggregate. When the mixing amount of slag and fly ash is 10%, the concrete presents the best flexural performance. Through the numerical loading test of the two-dimensional model for fly ash/slag concrete with cobble as coarse aggregate, it can be concluded that the change of the concrete follows the law of macromechanical properties.

Research on Evolution Characteristics of Shale Crack Based on Simultaneous Monitoring of Multi-Parameters

Meso-crack evolution mechanism of shale is a key factor affecting the mechanical properties of shale. In order to explore evolution laws of cracks in shale during loading, a meso-crack monitoring system, loading test equipment and an automatic ultrasonic data acquisition system were set up. On this basis, a set of experimental apparatus simultaneous monitoring multi-parameters of shale micro-crack was designed, and destruction experiments of shale samples with different bedding angles were carried out to find out evolution characteristics of cracks. The results show the following: (1) The designed apparatus can monitor ultrasonic, mechanical and video information simultaneously of crack evolution in the entire process of shale destruction under load to provide information for analyzing acoustic and mechanical characteristic responses of crack propagation at key time nodes. (2) With an increase in load, shale will undergo four stages of destruction: crack initiation, propagation, penetration and overall failure. In the course of these stages, acoustic characteristics and mechanical characteristics are in good agreement, which proves the validity of predicting rock mechanical parameters with acoustic data. (3) During the loading process of shale, the main amplitude of acoustic wave is more sensitive than mechanical parameters to the change of rock cracks. Research results have important theoretical reference value for evaluating wall stability of shale gas horizontal well with ultrasonic data.

The “Fight Bite” Saline Joint Loading Test: Effectiveness in Detecting Simulated Traumatic Metacarpophalangeal Arthrotomies

Background: The saline load test is routinely used to recognize other joints’ traumatic arthrotomies; however, there are currently no studies evaluating the novelty of this test for metacarpophalangeal joints (MCPJs). This study aimed to investigate the effectiveness and sensitivity of saline load testing in identifying the traumatic arthrotomies of the MCPJs using human cadavers. Methods: This was a cadaveric study of 16 hands (79 MCPJs). Traumatic arthrotomies were created using 11-blade stab-incisions, followed by blunt probing into the joint on the radial or ulnar side of the flexed MCPJs. A 3-mL syringe was used to inject intra-articular methylene-blue-dyed saline from the contralateral side. The volume at saline extravasation was recorded. Test sensitivity and factors influencing extravasation volume were assessed. Results: The mean (range) volume injected to identify arthrotomy of all MCPJs was 0.18 mL (0.1-0.4 mL). The mean volume to identify MCPJ arthrotomy of the thumb, index, long, ring, and small fingers was 0.16 mL (0.1-0.3 mL), 0.19 mL (0.1-0.3 mL), 0.21 mL (0.1-0.4 mL), 0.17 mL (0.1-0.3 mL), and 0.16 mL (0.1-0.3 mL), respectively. Cadaver age, laterality, and joint range of motion were not significantly associated with the injected volume at extravasation( P > .05, each). Injection volumes of 0.3 and 0.32 mL were required to detect arthrotomies at 95% and 99% sensitivities across all MCPJs. None of the MCPJs required > 0.4 mL to detect arthrotomy. Conclusions: Saline joint loading volumes to detect traumatic arthrotomy were similar for all MCPJs. Injection volumes of 0.32 mL is suggested for 99% sensitivity. Our findings provide the first report, to our knowledge, on intra-articular injection volumes expected to detect an arthrotomy of MCPJ. This is critical for further validation using in vivo clinical studies.

New anterior controllable antedisplacement and fusion surgery for cervical ossification of the posterior longitudinal ligament: a biomechanical study

OBJECTIVE The traditional anterior approach for multilevel severe cervical ossification of the posterior longitudinal ligament (OPLL) is demanding and risky. Recently, a novel surgical procedure—anterior controllable antedisplacement and fusion (ACAF)—was introduced by the authors to deal with these problems and achieve better clinical outcomes. However, to the authors’ knowledge, the immediate and long-term biomechanical stability obtained after this procedure has never been evaluated. Therefore, the authors compared the postoperative biomechanical stability of ACAF with those of more traditional approaches: anterior cervical discectomy and fusion (ACDF) and anterior cervical corpectomy and fusion (ACCF). METHODS To determine and assess pre- and postsurgical range of motion (ROM) (2 Nm torque) in flexion-extension, lateral bending, and axial rotation in the cervical spine, the authors collected cervical areas (C1–T1) from 18 cadaveric spines. The cyclic fatigue loading test was set up with a 3-Nm cycled load (2 Hz, 3000 cycles). All samples used in this study were randomly divided into three groups according to surgical procedures: ACDF, ACAF, and ACCF. The spines were tested under the following conditions: 1) intact state flexibility test; 2) postoperative model (ACDF, ACAF, ACCF) flexibility test; 3) cyclic loading (n = 3000); and 4) fatigue model flexibility test. RESULTS After operations were performed on the cadaveric spines, the segmental and total postoperative ROM values in all directions showed significant reductions for all groups. Then, the ROMs tended to increase during the fatigue test. No significant crossover effect was detected between evaluation time and operation method. Therefore, segmental and total ROM change trends were parallel among the three groups. However, the postoperative and fatigue ROMs in the ACCF group tended to be larger in all directions. No significant differences between these ROMs were detected in the ACDF and ACAF groups. CONCLUSIONS This in vitro biomechanical study demonstrated that the biomechanical stability levels for ACAF and ACDF were similar and were both significantly greater than that of ACCF. The clinical superiority of ACAF combined with our current results showed that this procedure is likely to be an acceptable alternative method for multilevel cervical OPLL treatment.

Experimental verification of punching shear resistance of flat slab fragments

The paper deals with the loading test results of an experimental reinforced concrete flat slab fragment, which was supported by an elongated rectangular column. The slab specimens were 200 mm thick and were designed without any shear reinforcement. By experimentally obtained punching shear resistance, the accuracy of the standard design models for prediction punching resistance was compared. The results of the experiments were also compared with the results of a numerical non-linear analysis performed in the Atena program.

Laboratory And Field Tests On A Prefabricated Steel-Bar Mesh-Panel System For Continuously-Reinforced-Concrete Pavement (CRCP)

The decline in the number of persons of working age is a social problem in Japan. This is a particularly serious concern for workers in the construction field; construction systems should be considered for productivity improvements. Prefabrication systems are an effective method for shortening construction cycles and times. In fact, various precast concrete members have been employed to realize more rapid construction and improvements in quality. Using precast concrete members is difficult because jointless roads are preferable for highway pavement. Continuously reinforced concrete pavement (CRCP), which has the advantages of concrete jointless construction and high ductility, is a suitable method for highway road construction. Typical Japanese highways built with CRCP reduce the amount of horizontal cracking by arranging transverse rebars at an angle of 60° to the main rebars. Note that rebar placement and bonding in conventional CRCP are troublesome and labor intensive owing to the long construction time required. We have developed prefabricated steel bar meshes for CRCP and can report some benefits relating to their practical application. To examine the fundamental properties of mesh panels, we conducted a laboratory experiment and a simulated field test. The primary concern of welded rebars are failures induced by cyclic loading. A flexural fatigue loading test using CRCP models was conducted. In addition, a comparative survey on conventional and prefabrication systems was performed in the simulated field test to quantify the constructability of CRCP and to observe the extent of cracking in concrete. This paper reports on our experimental investigation.