Experimental Study of Shear Performance of High-Strength Concrete Deep Beams with Longitudinal Reinforcement with Anchor Plate.

As a transfer member at the discontinuous place of vertical load, the deep beam has a complex stress mechanism and many influencing factors, such as compressive strength of concrete, shear span ratio, and reinforcement ratio. At the same time, the stress analysis principle of traditional shallow beams is no longer applicable to the design and calculation of deep-beam structure. The main purpose of this paper was to use the strut-and-tie model to analyze its stress mechanism, and to verify the applicability of the model. Nine high-strength concrete deep-beam specimens with longitudinal reinforcement with an anchor plate of the same size were tested by two-point concentrated loading method. The effects of shear span ratio (0.3, 0.6, and 0.9), longitudinal reinforcement ratio (0.67%, 1.05%, and 1.25%), horizontal reinforcement ratio (0.33%, 0.45%, and 0.50%), and stirrup reinforcement ratio (0.25%, 0.33%, and 0.50%) on the failure mode, deflection curve, characteristic load, crack width, steel bar, and concrete strain of the specimens were analyzed. The results showed that the failure mode of deep-beam specimens was diagonal compression failure. The normal section cracking load was about 15 to 20% of the ultimate load, and the inclined section cracking load was about 30~40% of the ultimate load. The shear span ratio increased from 0.3 to 0.9, and the bearing capacity decreased by 32.9%. When the longitudinal reinforcement ratio increased from 0.67% to 1.25%, the ultimate load increased by 42.6%. The shear span ratio and longitudinal reinforcement ratio have a significant effect on the bearing capacity of the high-strength concrete deep beams with longitudinal reinforcement with an anchor plate. The shear capacity of nine high-strength concrete deep-beam specimens with longitudinal reinforcement with an anchor plate was calculated by national standards, and the results were compared with the calculation results of the Tan-Tang model, the Tan-Cheng model, SSTM, and SSSTM. The analysis showed that the softened strut-and-tie model takes into account the softening effect of compressive concrete, and is a more accurate mechanical model, which can be applied to predict the shear capacity of high-strength concrete deep-beam members with longitudinal reinforcement with an anchor plate.

Analysis of Shear Model for Steel-Fiber-Reinforced High-Strength Concrete Corbels with Welded-Anchorage Longitudinal Reinforcement.

According to the shear capacity test results of six steel-fiber-reinforced high-strength concrete (SFHSC) corbels with welded-anchorage longitudinal reinforcement under concentrated load, the effects of shear span ratio and steel fiber volume fraction on the failure mode, cracking load and ultimate load of corbel specimens were analyzed. On the basis of experimental research, the shear transfer mechanism of corbel structure was discussed. Then, a modified softened strut-and-tie model (MSSTM), composed of the diagonal and horizontal mechanisms, was proposed, for steel-fiber-reinforced high-strength concrete corbels. The contributions of concrete, steel fiber and horizontal stirrups to the shear bearing capacity of the corbels were clarified. A calculation method for the shear bearing capacity of steel-fiber-reinforced high-strength concrete corbels was established and was simplified on this basis. The calculation results of the model were compared with the test values and calculation results of the GB50010-2010 code, the ACI318-19 code, the EN 1992-1-1 code and the CSA A23.3-19 code. The results showed that the concrete corbel with small shear span ratio mainly has two typical failure modes: shear failure and diagonal compression failure. With the increase in shear span ratio, the shear capacity of corbels decreases. Steel fiber can improve the ductility of a reinforced concrete corbel, but has little effect on the failure mode of the diagonal section. The calculated values of the national codes were lower than the experimental values, and the results were conservative. The theoretical calculation values of the shear capacity calculation model of the corbels were close to the experimental results. In addition, the model has a clear mechanical concept considering the tensile properties of steel-fiber-reinforced high-strength concrete and the influence of horizontal stirrups, which can reasonably reflect the shear transfer mechanism of corbels.

Experimental Investigation on Shear Capacity of Steel-Fiber-Reinforced High-Strength Concrete Corbels.

As short cantilever members, corbels are mainly used to transfer eccentric loads to columns. Because of the discontinuity of load and geometric structure, corbels cannot be analyzed and designed using the method based on beam theory. Nine steel-fiber-reinforced high-strength concrete (SFRHSC) corbels were tested. The width of the corbels was 200 mm, the cross-section height of the corbel column was 450 mm, and the cantilever end height was 200 mm. The shear span/depth ratios considered were 0.2, 0.3, and 0.4; the longitudinal reinforcement ratios were 0.55%, 0.75%, and 0.98%; the stirrup reinforcement ratios were 0.39%, 0.52%, and 0.785%; and the steel fiber volume ratios were 0, 0.75%, and 1.5%. According to the test results, this paper discusses the failure process and failure mode of corbel specimens with a small shear span/depth ratio and analyzes the effects of variables such as shear span/depth ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio, and steel fiber volume content on the shear capacity of corbels. The shear capacity of corbels is significantly affected by the shear span/depth ratio, followed by the longitudinal reinforcement ratio and the stirrup reinforcement ratio. Moreover, it is shown that steel fibers have little impact on the failure mode and ultimate load of corbels, but can enhance the crack resistance of corbels. In addition, the bearing capacities of these corbels were calculated by Chinese code GB 50010-2010 and further compared with ACI 318-19 code, EN 1992-1-1:2004 code, and CSA A23.3-19 code, which adopt the strut-and-tie model. The results indicate that the calculation results by the empirical formula in the Chinese code are close to the corresponding test results, while the calculation method based on the strut-and-tie model of a clear mechanical concept yields conservative results, and hence the related parameter values must be further modified.

A pilot study of the precision of digital intraocular pressure measurement during vitrectomy.

AIM: To evaluate the precision of digital intraocular pressure (IOP) measurement in silicone oil (SO) filled eyes during vitrectomy. METHODS: This is a retrospective, single-blind study. Patients who were diagnosed with retinal detachment and scheduled for vitrectomy with SO injection were consecutively enrolled. During the vitrectomy, IOP was digitally measured and then by a rebound tonometer (IcarePRO). The rebound tonometer readings were masked to the surgeons. The digitally measured IOP and that of rebound tonometer were compared, and the inter-methods agreement was assessed. The absolute deviation in IOP values between these two methods (ΔIOP) was also calculated, and correlations between ΔIOP and refractive status, lens status and levels of surgeons' experience were analyzed. RESULTS: A total of 131 patients (131 eyes) were recruited, with a mean age of 51.0±16.1y. There was no significant difference in IOPs between digital measurement and the rebound tonometer (15.6±4.3 vs 15.7±5.1 mm Hg; t=0.406, P=0.686). Intraclass correlation coefficients (ICC) analysis indicated a strong correlation between these two measurements (ICC=0.830, P<0.001). The mean ΔIOP was 2.0±1.9 mm Hg (range: 0-12.8 mm Hg), with 98 eyes (74.8%) had the ΔIOP within 3 mm Hg. ΔIOP was found to be negatively correlated with levels of surgeons' experience (r=-0.183; P=0.037), but not with the refractive status or lens status of the patients (both P>0.05). CONCLUSION: For experienced surgeons, the digital IOP measurement may be an acceptable technique for IOP measurement in SO filled eyes during vitrectomy. However, its use by inexperienced surgeons should be taken with caution.

Experimental Study on Shear Capacity of High Strength Reinforcement Concrete Deep Beams with Small Shear Span-Depth Ratio.

This study aimed to investigate the shear capacity performance for eight deep beams with HTRB600 reinforced high strength concrete under concentrated load to enable a better understanding of the effects of shear span-depth ratio, longitudinal reinforcement ratio, vertical stirrup ratio and in order to improve design procedures. The dimension of eight test specimens is 1600 mm × 200 mm × 600 mm. The effective span to height ratio l0/h is 2.0, the shear span-depth ratio λ is 0.3, 0.6 and 0.9, respectively. In addition, the longitudinal reinforcement ratio ρs is set to 0.67%, 1.05%, 1.27%, and the vertical stirrup ratio is taken to be 0%, 0.25%, 0.33%, 0.5%. Through measuring the strain of steel bar, the strain of concrete and the deflection of mid-span, the characteristics of the full process of shear capacity, the failure mode and the load deflection deformation curve were examined. The test results showed that the failure mode of deep beams with small shear span-depth ratio is diagonal compression failure, which is influenced by the layout and quantity of web reinforcement. The diagonal compression failure could be classified into two forms: crushing-strut and diagonal splitting. With decreasing of shear span-depth ratio and increasing longitudinal reinforcement ratio, the shear capacity of deep beams increases obviously, while the influence of vertical web reinforcement ratio on shear capacity is negligible. Finally, the shear capacity of eight deep beams based on GB 50010-2010 is calculated and compared with the calculation results of ACI 318-14, EN 1992-1-1:2004 and CSA A23.3-04, which are based on strut-and-tie model. The obtained results in this paper show a very good agreement with GB50010-2010 and ACI 318-14, while the results of EN 1992-1-1:2004 and CSA A23.3-04 are approved to be conservative.

[Dynesys and posterior decompression and fusion internal fixation for the treatment of lumbar degenerative diseases: a systematic review].

OBJECTIVE: Meta analysis was used to evaluate the efficacy and safety of Dynesys and posterior decompression and fusion internal fixation for lumbar degenerative diseases. METHODS: The computer was used to retrieve the Cochrane library, Medline, Embase, CNKI, Wanfang database and Chinese biomedical literature database; and the references and main Chinese and English Department of orthopedics journals were manually searched. All the prospective or retrospective comparative studies on the clinical efficacy and safety of Dynesys and posterior decompression and fusion internal fixation were collected, so as to evaluate the methodological quality of the study and to extract the data. The RevMan 5.2 software provided by Cochrane collaboration was used for systematic evaluation. RESULTS: A total of 9 clinical studies were included, including 3 prospective randomized controlled trials(RCT) and 6 retrospective controlled observational studies, which included 692 patients, with 336 cases in Dynesys group, and 356 cases in posterior decompression and fusion internal fixation (PLIF) group. The results showed that compared with PLIF, Dynesys system significantly decreased operation time(P<0.01), intraoperative blood loss (P<0.01). Both Dynesys and PLIF groups experienced improved ODI and back/leg pain VAS scores at final follow-up, and no statistically significant difference was noted according to the two surgical procedures(P>0.05). Dynesys could remain the range of motion (ROM) of surgical segments with less increased ROM of adjacent segments compared with that of PLIF group(P<0.01). Regarding the disc height of surgical segments, no statistically significant difference was noted according to the two groups(P>0.05), but postoperative complications incidence rate in PLIF group was higher than that in Dynesys group (P<0.05). CONCLUSIONS: Both Dynesys system and PLIF can improve clinical outcomes of lumbar degenerative diseases effectively. Compared with PLIF, Dynesys could remain the range of motion(ROM) of surgical segments with less increased ROM of adjacent segments and lower complication incidence rate. But the ability to prevent adjacent segments degeneration needs more RCTs with long-term follow-up to confirm.

Statistical interpolation method of turbulent phase screen.

A relative displacement between the grid points of optical fields and those of phase screens may occur in the simulation of light propagation through the turbulent atmosphere. A statistical interpolator is proposed to solve this problem in this paper. It is evaluated by the phase structure function and numerical experiments of light propagation through atmospheric turbulence with/without adaptive optics (AO) and it is also compared with the well-known linear interpolator under the same condition. Results of the phase structure function show that the statistical interpolator is more accurate in comparison with the linear one, especially in the high frequency region. More importantly, the long-exposure results of light propagation through the turbulent atmosphere with/without AO also show that the statistical interpolator is more accurate and reliable than the linear one.