Impact of the reinforcement layout on the load capacity of reinforced concrete half-joints

A reinforced concrete half-joint beam has a complex geometry that includes both a locally disturbed nib region and a full depth section. While this configuration simplifies the design and construction procedures, half joint structures rely on the internal steel reinforcement to transfer force from the nib into the bulk of the beam. When assessing existing reinforced concrete half-joints, engineers can be confronted with internal reinforcement layouts that do not correspond to the as-designed drawings and/or do not comply with current design practice. Bars may be missing or the location, percentage and spacing of the steel reinforcing bars may be non-compliant. To provide a better understanding of the contribution of the internal steel reinforcing bars found in a typical half joint detail, an experimental test program on full-scale half-joint beams was undertaken. Four different scenarios were tested to identify the impact of specific reinforcing bars. A reference specimen was designed in accordance with existing practice. The reference beam, and beams with either missing diagonal reinforcement, missing horizontal reinforcement or a reduced amount of shear reinforcement were tested. All the beams exhibited nib failures with the exception of the beam where the shear reinforcement was reduced. In this case, the failure mode changed from a nib failure to a full-depth failure. The results indicated that if certain bars are missing the overall load bearing capacity of a half-joint could be approximately 40% lower than that of a properly designed detail, but that a redistribution of forces was noted.Engineering and Physical Sciences Research Council through the Project ‘Reinforced concrete half-joint structures: Structural integrity implications of reinforcement detailing and deterioration’ [Grant no. EP/K016148/1

Impact of material deterioration on the strength of reinforced concrete half-joint structures

During the 1960’s and 1970’s a number of reinforced concrete (RC) bridges were constructed with ‘half-joints’ introduced into bridge decks. A half-joint is a particular type of RC structure that was introduced into bridge decks as a means of simplifying the design and construction operations. However, a major disadvantage is that there are problems associated with leakage of water through the joint leading to concrete deterioration and corrosion of the reinforcement. When assessing the integrity of existing half-joint structures, determining the influence of material deterioration and/or repair works is a challenge as current code provisions or guidelines do not provide guidance on how to take any associated strength losses into consideration. This paper focusses on the impact of changes in the material properties (such as compressive strength, yield strength of the reinforcement, reinforcement bar diameter, etc.) on the load bearing capacity of reinforced half-joint structures. The vulnerability of a typical half-joint design to these changes is analysed using finite element models. The results allow designers, assessors and decision makers to better quantify the impact of observed deterioration phenomena on the predicted strength of the studied half-joint.This is the author accepted manuscript. The final version is available from the International Association for Bridge and Structural Engineering via http://dx.doi.org/10.2749/22213781581562275

Bond behaviour of reinforcing bars in cracked concrete

Due to the relatively low tensile strength of concrete, cracks are inherent in reinforced concrete structures. A common cause of cracking is the corrosion of internal steel reinforcement, a deterioration process that can affect the bond behaviour and anchorage capacity of reinforcing bars. Corrosion leads to a reduction of the reinforcing bar diameter, the formation of a weak layer of corrosion products around the bar and expansive forces on the surrounding concrete (that can lead to cracking). In the past, the impact of corrosion on bond has been investigated by means of accelerated corrosion tests. However, the more fundamental impact of cracking as distinct from corrosion products on the bond reduction is still not fully understood. This study applies a novel test method to investigate the bond behaviour of reinforcing bars in cylindrical cracked reinforced concrete specimens. The influence of the number of cracks, crack orientation, confinement and concrete cover are investigated. The results indicate a significant loss of bond strength for single cracked specimens. This reduction becomes as high as 65% for double cracked specimens in the absence of confinement. It is shown that the crack orientation with respect to the rib pattern is of minor influence, but the concrete cover and confinement play a significant role in the obtained bond characteristics.The authors would like to gratefully acknowledge the financial support of the UK Engineering and Physical Sciences Research Council (EPSRC) through the EPSRC Project ‘Reinforced concrete half-joint structures: Structural integrity implications of reinforcement detailing and deterioration’ [Grant no. EP/K016148/1].This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.conbuildmat.2015.06.04

Correlation between surface crack width and steel corrosion in reinforced concrete

Reinforced concrete structures are subjected to weather conditions, chemical attack and other sources of deterioration that can affect their performance. In particular, corrosion of the internal steel reinforcement is considered to be one of the main causes of structural deterioration. A possible consequence of corrosion is cracking of the surrounding concrete. Visual inspections are often used to inform asset management strategies. Finding a relationship between cracks that are visible on the outer surface of a structure and corrosion of the internal reinforcement can be helpful when making assessment decisions. To this end, unconfined cylindrical concrete specimens with an embedded steel bar have been subjected to accelerated corrosion using an impressed current density of 200µA/cm2, leading to steel mass losses between 5-24%. This paper discusses the measured correlation between corrosion-induced surface crack widths and degree of reinforcement corrosion. The tests highlighted some limitations of a set-up that is commonly adopted for accelerated corrosion and concentric pull-out bond testing. The findings of this study represent a first step towards the standardisation of accelerated corrosion testing procedures using an impressed current.</jats:p

Strut-and-tie models for deteriorated reinforced concrete half-joints

A reinforced concrete half-joint bridge consists of suspended span dapped-end beams or a full-width deck supported on the nibs of abutments or adjacent beams. The design of their disturbed regions is traditionally performed by means of strut-and-tie modelling. The design provisions found in standards and codes can be used for the assessment of existing structures with minor adjustments. However, current documents provide limited guidance on the incorporation of deterioration aspects such as corrosion, insufficient anchorage lengths, and crack formation. Experiments performed on 12 half-joint beams demonstrated the effects of single defects, but synergistic effects were also found to exist and might lead to much higher reductions than expected from the sum of individual defects. These results were compared to different strut-and-tie models (STMs) and the application of STMs to achieve the highest lower bound estimate of the load carrying capacity is discussed. For the beams studied in the current work, the predictions based on codes and standards, combined with appropriate methods to incorporate deterioration effects, led to safe load bearing capacity estimates. However, the developed STMs seem to be, in some instances, unable to pick up alternative load paths that develop as soon as the capacity of a certain tie is reached. Hence the actual capacities might be higher than what is obtained from the STM calculations

Corrosion-induced cracking and bond strength in reinforced concrete

Corrosion of the steel reinforcement is among the main causes of deterioration in concrete structures. Measures of corrosion levels are typically used to evaluate the subsequent reduction in steel-to-concrete bond, but results lack accuracy. In this study, a new assessment approach based on surface cracks was investigated. Specimens were subjected to accelerated corrosion using an impressed current. With a novel sealing method, mass losses were decoupled from concrete cracking. The results indicate that surface crack widths can be better indicators of bond degradation than corrosion levels. The findings can lead to more accurate assessments and reduced maintenance costs of infrastructure

Bond behaviour of austenitic stainless steel reinforced concrete

Stainless steel reinforced concrete has seen a large increase in usage in recent years, in response to the ever-increasing demands for structures and infrastructure to be more durable, efficient and sustainable. Currently, existing design standards advise using the same design rules for stainless steel reinforced concrete as traditional carbon steel reinforced concrete, owing to a lack of alternative information. However, this is not based on test or performance data. As such, there is a real need to develop a full and fundamental understanding of the bond behaviour of stainless steel reinforced concrete, to achieve more sustainable and reliable design methods for reinforced concrete structures. This paper investigates the bond behavior of stainless steel reinforced concrete and compares the performance to traditional carbon steel reinforced concrete, through experimental testing and analysis. It also compares the results to existing design rules in terms of bond strength, anchorage length and lap length. It is shown that stainless steel rebar generally develops lower bond strength with the surrounding concrete compared with equivalent carbon steel reinforcement. Moreover, it is shown that existing design codes are very conservative and generally underestimate the actual bond strength by a significant margin. Therefore, following detailed analysis, it is concluded that current design rules can be safely applied for stainless steel rebar, although more accurate and efficient methods can be achieved. Hence, new design parameters are proposed reflecting the bond behaviour of stainless steel rebar, so that more efficient designs can be achieved. Moreover, a summary of recommendations for the codes of practice is provided

Klinefelters Syndrome: Change in T-Scores with Testosterone, Bisphosphonate, and Vitamin D Treatment over 6 Years

Background: Klinefelter's syndrome (KS) is characterized by extra X chromosomes and features of primary hypogonadism including osteopenia and osteoporosis. Testosterone therapy (TTh) is widely used to treat men with KS and low serum testosterone/hypogonadal symptoms, though studies on its efficacy in improving bone density show varied outcomes. Materials and Methods: We studied the effects of TTh, bisphosphonates, and vitamin D/calcium in 38 men with KS and low testosterone, hypogonadal symptoms, and T-scores consistent with osteoporosis. Our aim was to investigate at the end of follow-up (median: 87 months, range: 27-147 months), associations between age, baseline total testosterone, and T-scores, and change in T-scores after treatment. Results: At final assessment, all men had T-score values outside the osteoporotic range (-1.1 standard deviation [SD],-1.8 SD). Baseline age but not median baseline testosterone appeared associated with change in T-score and T-score at final assessment. All men had dual-energy X-ray absorptiometry every 6 months and demonstrated continued improvement in T-scores after 3 months and up to 72 months. Baseline age and T-scores (stratified by median) were associated with change in T-score at final assessment. Compared with men ≥51 years, those aged <51 years showed significantly greater improvement in T-scores between 6 and 30 months. Men with worse T-score values (<3.7 SD) showed significantly greater improvement at every time point up to 36 months. Our results indicate that TTh, bisphosphonates, and vitamin D/calcium improve osteoporosis although there is a need to better understand the effects of the individual therapies, age, and baseline T-score on treatment efficacy

Testosterone replacement therapy: association with mortality in high-risk patient subgroups

Data availability statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.[Correction added on 12 January 2024, after first online publication: Figure 1 updated in this version.]Copyright © 2023 The Authors. Objectives: We describe studies determining the association between testosterone therapy (TTh) and mortality. Materials & methods: We used a registry database of 737 men with adult-onset testosterone deficiency defined as presenting with low serum total testosterone (TT) levels ≤12.1 nmol/L and associated symptoms over a near 10-year follow-up. We compared associations between testosterone undecanoate (TU), cardio-metabolic risk factors and mortality using non-parametric statistics followed by separate Cox regression models to determine if any association between TU and morality was independent of age and cardio-metabolic risk factors. Finally, the association between TU and mortality was studied in men stratified by cardio-metabolic risk. Results: During a median follow-up interquartile range (IQR) of 114 (84–132) months, 94 of the 737 men died. TU (ref: non-treatment) was associated with mortality; hazard ratio = 0.23, 95% confidence intervals = 0.14–0.40. Cox's regression models showed the above association to be independent of baseline age, waist circumference, hemoglobin A1c, lipids, blood pressure, smoking, and type 2 diabetes. These variables remained associated with mortality. We finally stratified the men by the high-risk baseline variables and established that the association between mortality and TU was only evident in men at higher risk. A possible explanation could lie with the “law of initial value,” where greater improvements are evident following treatment in patients with worse baseline values. Conclusions: This study with long follow-up confirms that TTh is associated with lower mortality in men with adult-onset TD. This association was evident only in men with greater cardio-metabolic risk factors who demonstrated greater benefit.North Staffordshire Medical Institute. Grant Number: PID-200078

Testosterone Therapy in Adult-Onset Testosterone Deficiency: Hematocrit and Hemoglobin Changes

Objective: Hematocrit (HCT)/hemoglobin (Hb) ratio in (%/g/dL) is around 3, with high fidelity between measured and derived Hb (applying the conversion using HCT) in various pathologies. We examined changes in HCT and Hb values and HCT/Hb, compared with baseline, in men with adult-onset testosterone deficiency (TD) given testosterone therapy (TTh). Materials and Methods: Data were analyzed from an observational, prospective registry study at various time points in 353 men with adult-onset TD receiving testosterone undecanoate (median follow-up: 105 months). After establishing baseline HCT/Hb, we compared (cf. baseline) changes in HCT, Hb, and HCT/Hb at 12, 48, 72, and 96 months. Regression analyses determined predictors of HCT and Hb change. Results: TTh was associated with ( p < 0.0001) increases in median HCT and Hb; 44% to 49% and 14.5 to 14.9 g/dL at final assessment, respectively. Regression analyses showed that HCT change was associated with baseline HCT and testosterone levels, while Hb change was associated with baseline Hb, HCT, and testosterone levels. In the total cohort and subgroups, HCT/Hb increased significantly at all time points ( p < 0.0001, cf. baseline) with over 90% of men demonstrating increases. Linear regression showed that the ratio of HCT change/Hb change (i.e., difference between HCT at the various time points and baseline value/difference between Hb at the various time points and baseline value), following TTh at each time point was higher than the baseline HCT/Hb ratio. Conclusion: HCT increase was greater than we anticipated from the established HCT/Hb of 3. We speculate that increased erythrocyte life span with associated higher Hb loss via vesiculation could account for our observation. This could have a bearing when using HbA1c as an indicator in men with adult-onset TD on TTh