Development Length Of Reinforcement Research Articles

The development length of tensile reinforcement embedded in High Volume Fly Ash-Self Compacting Concrete (HVFA-SCC)

• The development length of reinforcement in concrete is affected by the concrete types. • The observed bond failure in the beams with and without stirrups are splitting and slippage, respectively. • Stirrup increases the bond strength of HVFA-SCC to the reinforcement. • The proposed model gives a good estimation to the experimental results. This research evaluates the development length of tensile reinforcement in High Volume Fly Ash-Self Compacting Concrete (HVFA-SCC), which is a new type of concrete combining SCC and HVFA concepts. The development length of reinforcement is an important supportive property applied to HVFA-SCC, as a structural element. To ensure good load transfer between reinforcement and concrete, a sufficient development length is essential, with the length requirements being specified in the codes, formulated based on the bond strength of normal concrete experiments. Previous studies discovered that the bond strength of HVFA-SCC was greater than normal concrete, subsequently affecting the development length requirements. Therefore, this study proposes an equation to determine the development length required for reinforcement embedded in HVFA-SCC beams. Data were obtained from beam analysis, with several tests being carried out on 42 beams having the dimensions 150 × 250 mm and length 2 m, respectively. The investigated parameters were the reinforcement diameter and splice lengths, as well as the confinement effects of stirrups along the lap splice. The proposed equation was then compared with those suggested in the literature for other types of concrete. The results showed that the proposed equation gives a closer estimation to the experimental results compared to previous equations suggested in the literature.

Unified approach for reinforcement development length using the partly cracked elastic stage for bond strength

Current structural design codes in the United States treat the development of straight bars/lap splices, standard hooks, and deformed headed bars with separate equations. The fib Model Code 2010, on the other hand, uses a more unified approach. Recent changes to the standard hook and headed bar equations in the ACI 318–19 Building Code Requirements for Structural Concrete have sparked conversation about the discrepancies between ACI 318–19 and the AASHTO LRFD Bridge Design Specifications within the bridge design community. The objective of this research was to develop and validate a unified approach for the design/evaluation of reinforcement anchorage. A procedure based on the partly cracked elastic stage of bond was proposed. The proposed procedure was validated with 1006 tests from the literature.

Bond of FRP bars in air-entrained concrete: Experimental and statistical study

The combined use of Fibre Reinforced Polymer (FRP) and Air-Entrained Concrete (AEC) can be an alternative to traditional steel-reinforced concrete as this system is less affected by the corrosion of the reinforcement and by the freeze-thaw cycles induced concrete degradation. However, the viability of this system hinges on the bond performance of the reinforcing bars. A total of 236 pull-out specimens were prepared and tested to study the effect of air-entraining admixtures (AEA) on the bond behaviour of FRP bars to concrete with varying compressive strengths. Failure modes and bond stress-slip curves were reported and discussed. The bond energy, calculated as the area under the bond stress-slip diagram, was also analyzed. The experimental peak bond stresses (bond strength) were compared to the theoretical ones characterized by the formula proposed for steel bars by the Model Code 2010. In addition, the statistical significance of the effect of AEA on bond characteristics was determined, yielding a reduction factor to account for the effect of AEA on bond strength. The test results show that the bond strength of FRP bars in AEC was statistically significantly lower than in normal concrete. However, the decrease is sufficiently small that could be accounted for, during the design stage, by merely increasing the reinforcement development length.

Anchorage length of reinforcing bars in tension: an assessment of the Australian Standard AS 3600:2018

When designing a reinforced concrete member for strength, ductility and robustness, it is essential that a sufficient length of reinforcement is developed on both sides of a critical section in a zone of tension. The specifications of the existing codes of practice for calculating the development length of reinforcement are statistically based on test data mostly from small-scale pull-out and beam specimens, and their applicability outside the range of the test data is uncertain. This paper describes an experimental research program to assess the effects of different structural parameters on the development length requirements for modern high strength steel reinforcing bars, including the case of lapped splices in large-scale reinforced concrete members in bending. The factors of safety obtained in the tests are assessed according to the Australian Standard (AS3600:2018) provisions for the anchorage length of reinforcing bars in tension and also in terms of attainable average bond stress in different anchorage conditions. The study has revealed that modification(s) to two of the coefficients included in the provisions of AS3600:2018 would provide a more consistent and reliable factor of safety for the anchorage of reinforcement in large-scale concrete members, including at lapped splice locations.

Experimental assessment of fire-exposed RC beam-column connections with varying reinforcement development lengths subjected to column removal

This paper describes an experimental investigation into the behaviour of RC beam-column connections under a column removal scenario induced by fire. A purpose-built hybrid heating furnace is employed to carry out the fire tests on five RC connections with varying reinforcement development lengths, with and without cooling effects. The thermal response of the RC connection specimens, including the temperature field and the axial force-furnace temperature curves, is firstly described. Subsequently, push-down tests are carried out on the beam-column connections, and the horizontal support reactions are closely monitored using a specially-designed sensor system. Based on the experimental results, the joint vertical load-displacement and bending moment-rotation relationships are presented, together with an account of the failure modes observed. The mechanical behaviour is discussed in detail, including the tying and rotation capacity provided by the connection specimens, with emphasis on the effect of the reinforcement development length as well as the heating regime. The experimental capacity interaction curves are also compared with the theoretical prediction for ambient condition, and employed to carry out a detailed examination of the underlying failure mechanisms. Finally, the findings are used to provide practical recommendations for enhancing the structural robustness of structural configurations of the form considered in this study.

Teaching learning-based optimization for design of cantilever retaining walls

A methodology based on Teaching Learning-Based Optimization (TLBO) algorithm is proposed for optimum design of reinforced concrete retaining walls. The objective function is to minimize total material cost including concrete and steel per unit length of the retaining walls. The requirements of the American Concrete Institute (ACI 318-05-Building code requirements for structural concrete) are considered for reinforced concrete (RC) design. During the optimization process, totally twenty-nine design constraints composed from stability, flexural moment capacity, shear strength capacity and RC design requirements such as minimum and maximum reinforcement ratio, development length of reinforcement are checked. Comparing to other nature-inspired algorithm, TLBO is a simple algorithm without parameters entered by users and self-adjusting ranges without intervention of users. In numerical examples, a retaining wall taken from the documented researches is optimized and the several effects (backfill slope angle, internal friction angle of retaining soil and surcharge load) on the optimum results are also investigated in the study. As a conclusion, TLBO based methods are feasible.

Development Length in Reinforced Concrete Structures Exposed to Steel Corrosion: A Correction Factor for AS3600 Provisions

In reinforced concrete structures, reinforcement corrosion induces concrete cracking and leads to a reduction in both the steel cross-section and the steel-concrete bond strength and ultimately affects the development length. In this paper, a new correction factor is proposed to calculate the development length of reinforced concrete structures prone to corrosion. A scalar bond damage parameter is introduced to relate bond strength reduction to corrosion. The new model agrees well with all experimental results found in the literature. The bond damage parameter is further used as a correction factor modifying the AS3600 provisions for the development length of reinforcement in reinforced concrete structures located in a saline environment. The relationship between steel-concrete bond damage and corrosion induced concrete cracking is also discussed.

Splice length of prestressing strands in field-cast UHPC connections

The development length of reinforcement embedded into ultra-high performance concrete (UHPC) can be significantly shorter than the lengths normally associated with conventional concrete. Shortening the development length of prestressing strands can allow for a redesign of some structural systems, including spliced girder and continuous-for-live-load bridges. UHPC, when used in field-cast connections between prefabricated elements, can create robust connections which emulate monolithic components. This study investigated the development length of 12.7- and 15.2-mm diameter untensioned prestressing strands embedded in steel fiber and PVA fiber reinforced UHPC. The volumetric fiber content was 2 %. A novel tension test method allowed for replication of the stress state that occurs when strands are lap spliced within a connection between two linear elements. The results suggest that, for the steel fiber reinforced UHPC, the 12.7-mm diameter strands can be fully developed within 51 cm and the 15.2-mm diameter strands can be fully developed in approximately 61 cm. The 12.7-mm diameter strands can be fully developed in the PVA fiber reinforced UHPC in approximately 91 cm. Applying UHPC to create lap splice connections of prestressing strands may allow for increased structural efficiency and increased structural redundancy through the use of simple, non-congested, non-post-tensioned connection details.

반복하중이 작용하는 고강도 모르타르 충전식 슬리브 철근이음에 대한 강성 평가

본 논문에서는 반복하중이 작용하는 고강도 모르타르 충전식 슬리브 철근이음의 강성에 대한 합리적인 검토를 하기 위하여 100여개 고강도 모르타르 충전식 슬리브 철근이음의 실험데이터를 이용하여 슬리브 철근이음이 보유하고 있는 구조인자가 반복 하중이 작용하는 슬리브 철근이음의 강성에 미치는 효과를 파악하였고, AIJ 규준에 정해져 있는 강성 등급을 충족시키는 최소한 의 조건에 대하여 평가한 결과, SD350과 SD400 철근을 매입한 모르타르 충전식 주물 슬리브 철근이음에서 <TEX>$f_{g^*}$</TEX>(L/d)가 470MPa 이상이 된다면 AIJ 규준의 SA급 강성, <TEX>$f_{g^*}$</TEX>(L/d)가 340MPa 이상이 된다면 AIJ 규준의 A급 강성을 최종파괴형식과 슬리브 형상에 상관없이 확보할 수 있는 것으로 나타났다. 또한 SD500 철근을 매입한 모르타르 충전식 슬리브 철근이음에서 주물슬리브와 강관 슬리브를 사용한 경우는 <TEX>$f_{g^*}$</TEX>(L/d)가 400MPa 이상이 된다면 AIJ 규준의 A급 강성을 확보할 수 있는 것으로 나타났다. In order to make a more reasonable evaluation on the stiffness of the high-strength mortar-filled sleeve bar splices under cyclic loading, we investigated and analyzed the existing experiment data of 106 full-sized reinforcing bar splices with test variables such as compressive strength of mortar, development length of reinforcement and sleeve type, etc. The following were found: 1) If mortar and the reinforcement development length with <TEX>$f_{g^*}$</TEX>(L/d) of more than 340 is used, the cast iron sleeve bar splices for SD350 and SD400 will have the stiffness of higher than A class of the AIJ code. 2) If mortar and the reinforcement development length with <TEX>$f_{g^*}$</TEX>(L/d) of more than 400 is used, the cast iron sleeve splices and pipe sleeve splices for SD500 will have the stiffness of higher than A class of the AIJ code.

고강도 모르타르를 충전한 기계적 슬리브 철근이음에 대한 단조가력 하에서의 강성 평가

The purpose of this study is to evaluate the stiffness of the mechanical sleeve reinforcement splices filling high-strength mortar under monotonic loading. For this objective, we analyzed and compared the previous test data of 189 actual-sized mortar-filled sleeve bar splices specimens, including the reinforcing bar splices prepared and tested by the author. The paper results indicated that the minimum values of compressive strength of mortar() multiplied by the ratio of reinforcement development length to bar diameter(L/d) were suggested for holding the stiffness of the mortar-filled sleeve reinforcement splices required in AIJ code.