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1

A study on the deflection and crack layout in a hollow slab bridge

Wang Songtao, Wang Dawei

Archives of Civil Engineering

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2023

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Vol. 69, nr 3

541--555

EN

This paper conducts research based on the hollow slab members in the reconstruction and expansion project of expressways, two types of numerical finite element models with and without considering bond-slip relationship of reinforcement and concrete are established, and verified by tests. The distribution characteristics of crack spacing in reinforced concrete beams are studied. The results show that the bond-slip characteristics of reinforced concrete have little effect on the load-deflection characteristics of 8m hollow slab beam. Due to the influence of the bond-slip relationship of reinforced concrete, the load-deflection curve is partially serrated, while without considering the bond-slip relationship of reinforced concrete, the load-deflection curve is smooth. In the numerical model without considering the bond-slip characteristics, almost all damage occurs in the longitudinal direction, and the distribution characteristics of cracks can’t be accurately determined. Regardless of whether the bond-slip is considered or not, the macroscopic characteristics of the stress distribution is: smaller near the support and larger at the mid-span. As secondary flexural cracks expand, models with and without consideration of bond-slip characteristics can’t calculate crack spacing based on the stress distribution characteristics of the reinforcement.

2

Experimental and numerical evaluations of the bond behaviour between ribbed steel rebars and concrete

Biscala Hugo C.

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e159, 2023

EN

The study of interfacial behaviour between ribbed steel rebars and concrete is a subject that has been widely studied. However, the definition of the bond stress distribution throughout the embedded length of the steel rebar is still controversial due to the difficulty of experimentally obtaining such distribution for a fixed load magnitude. It is also undeniable its relevancy for the better understanding and model reinforced concrete (RC) structures. So, the definition of the local behaviour between the ribbed steel rebar and concrete is critical to correctly simulate the adherence between both materials. In this matter, the local bond-slip models recommended in codes seem to satisfy some researchers while others suggest prudence in using them. Therefore, only choosing the correct bond-slip relationship may lead to exact interpretations and conclusions of the structural behaviour of a concrete structure but with the existing different bond-slip types, researchers can be misled inadvertently. This work aims to clarify some of these aspects by numerically simulating several pull-out tests under different conditions and checking their influence (or not) on real-scale specimens. After the validation of the numerical model through a proposed new bond-slip relationship, other parameters were studied also. Although the type of the bond-slip relationship influences the detachment of the steel rebar from the concrete, the yielding of the former material was found to be the main parameter that masks the differences in the behaviour of real-scale RC structures when different types of bond-slip relationships were considered in the numerical simulations.

3

Effect of bond conditions on local bond-slip relationships of ribbed bars in high performance self-compacting concrete

Dybel Piotr

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 4

1399--1408

EN

The bond of concrete to steel reinforcing bars is the basis for the concept of reinforced concrete as a construction material. One of important bond-related issues is the bond strength-bar slip relation, which has an influence on the failure mode and rotation of structural joints. This relation can be predicted by bond–slip models and it depends on the bond behaviour at the reinforcement–concrete interface. However, the currently-known bond-slip models offer limited applications to well-studied normal concretes only. This article proposes local bond–slip relationships for high performance self-compacting con-crete (HPSCC) taking into account the quality of bond conditions. The studies were per-formed on specimens made of four different high performance self-compacting concrete mixes with varying contents of silica fume. Since the specimens had total heights of 480, 800 and 1600 mm, it was possible to measure the changes of the bond at individual levels. The results were next compared to those obtained for samples made of vibrationally-compacted high-performance concrete (HPC). It was demonstrated that the bond-slip model for normal concretes seems to underestimate the bond stiffness and ultimate bond strength for the HPSCC and HPC mixtures. Moreover, it was proven that a change of the quality of bond conditions has an effect on the local bond-slip relationship. Finally, local bond-slip relation-ships were presented separately for HPSCC and HPC with respect to the quality of bond conditions

4

Badania przyczepności betonu zwykłego i geopolimerowego do pręta stalowego

Seshu D. R.

Cement Wapno Beton

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2018

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R. 21/83, nr 2

89--97

PL

Beton geopolimerowy jest jednym z nowoczesnych materiałów budowlanych zastępujących klasyczny beton z cementu portlandzkiego. Przeprowadzono wiele badań dotyczących zastosowania betonu geopolimerowego jako materiału budowlanego, jednak nieliczne z nich dotyczą jego zastosowania w konstrukcjach. Praca przedstawia porównanie wyników wytrzymałości wiązania stali z betonem zwykłym i geopolimerowym. Przeprowadzono badania przyczepności metodą „pull out” na 27 belkach o wymiarach 100×100×200 mm3, wykonanych z trzech różnych klas betonu geopolimerowego, a mianowicie M20, M35 i M50, zbrojonych prętami TMT o średnicy 16 mm. Uzyskane wyniki badań pozwoliły na opracowanie równania opisującego przyczepność betonu geopolimerowego do stali, którego poprawność zweryfikowano doświadczalnie. Znormalizowaną funkcję naprężenia przyczepność-przemieszczenie betonu geopolimerowego można w przybliżeniu przedstawić jako krzywą dwóch zmiennych.

EN

One of the new construction materials evolved as a replacement of Ordinary Portland cement concrete is geopolymer concrete. Many investigations have been done to develop geopolymer concrete as a material but studies on structural use of geopolymer concrete are very rare. This paper presents the experimental investigation on the band behaviour of normal and geopolymer concrete. The band strength behaviour of 27 geopolymer concrete prisms of size 100x100x200 mm3 of grades M20, M35 and M50 reinforced with 16 mm TMT rod is studied using pull out tests. An equation for the bond strength of geopolymer concrete is obtained from the experimental results and is also validated. The normalized bond-slip behaviour of GPC can be idealized as the curve of two variables.

5

Full-scale field experimental investigation on the interfacial shear capacity of continuous slab track structure

Dai G., Su M.

Archives of Civil and Mechanical Engineering

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2016

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Vol. 16, no. 3

485--493

EN

This paper presents the experimental observations and results of six full-scale field ballastless track structure specimens, and tested under longitudinal and transverse shear load. The tests aimed to examine the interfacial shear capacity of the continuous slab track structure and investigate the interfacial bond–slip behaviour. The results show that bond strength of the two interfaces which were on the top and bottom of mortar layer, respectively, have a large difference. Until the top interface of the mortar layer fractured, no slip displacement was observed in the bottom interface. In addition to the experimental study, a finite element model using nonlinear interface elements was employed to simulate the tests. The numerical calculated capacity agreed well with the experimental results, showing that the proposed bond–slip law is reliable. Finally, the track slab's evenness with the bond–slip effect under the dynamic load was studied.

6

Influence of internal cracks on bond in cracked concrete structures

Pędziwiatr J.

Archives of Civil and Mechanical Engineering

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2008

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Vol. 8, no 3

91-105

EN

The bond between concrete and steel bars is of fundamental importance to deformation characteristics of cracked concrete structures. It has been extensively studied for many years, particularly from the early 1970s. But the results of the studies seem to be inadequate for concrete structure analysis. They are not renected in engineering practice and codes. This is mainly due to the fact that most of the experimental research has been conducted on specimens with very short embedded length. The behaviour of such specimens differs very much from that of a real cracked concrete structure with a tension zone. One of the most important differences is the presence of internal cracks in the real member. Internal cracks arise close to the steel bars and develop towards the member's edge. Although they are invisible while inside the member, they change the strain distribution in the steel along the bars and so atffect the bond. When they reach the edge, they become so-called 'secondary cracks'. Internal cracks are responsible for a large scatter in crack width and spacing. Research into internal cracking and its effect on bond can provide a convincing explanation of the phenomenon of irregular concrete strain distribution in a reinforced cross section under uniaxial tension. In Wrocław University of Technology's Institute of Building Engineering, specimens were designed and prepared specifically for the direct observation of internal cracks and the measurement of steel and concrete strains. Such specimens and experiments are more expensive and timeconsuming but the results renect the behaviour of real concrete members much better. The experimental data confirmed the theoretical predictions and allowed us to make the model more accurate.

PL

Przyczepność jest podstawowym mechanizmem umożliwiającym przekazywanie siły ze stali na beton w zarysowanych elementach żelbetowych. Dotychczasowe intensywne studia teoretyczne i eksperymentalne na temat przyczepności nie przynoszą praktycznych efektów w odniesieniu do analizy zachowania się rzeczywistych elementów konstrukcyjnych. Jest to skutek używania nieadekwatnych elementów do prowadzenia badań i w konsekwencji przyjmowanie blędnych koncepcji teoretycznych. Badania na elementach zaprojektowanych i wykonanych w Instytucie Budownictwa Politechniki Wrocławskiej pozwoliły zdecydowanie lepiej odwzorować warunki pracy rzeczywistych konstrukcji. W szczególności umożliwiły one określenie roli rys wewnętrznych w elemencie. Ich powstanie jest odpowiedzialne za różnice w odkształcalności elementów osiowo rozciąganych i zginianych. W elementach konstrukcyjnych o dużych otulinach są one przeważnie niewidoczne, ale już od chwili powstania modyfikują przebiegi odkształceń. Dzieki stwierdzeniu ich roli można wyjaśnić szereg paradoksów z którymi ma się do czynienia w analizie zarysowanych konstrukcji żelbetowych.