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1

Machine learning models for cracking torque and pre‑cracking stiffness of RC beams

Shenggang Chen, Quanquan Guo, Yingying Zhang, Hexiang Hu, Bei Shen

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e6, 2023

EN

The torsional behavior of RC beams is a complex work involving interactions of different design parameters and mechanisms. Considering the limitations and lower accuracy of traditional calculation theories, two machine learning models, including artificial neural network (ANN) model and random forest (RF) model, were applied for the frst time to predict the cracking torque and initial or pre-cracking torsional stiffness of RC beams. A comprehensive database consisting 159 experimental results of RC beams with solid or hollow sections was compiled, with input variables including dimension parameters of cross-section, compressive stress of concrete, elastic modulus and strength ratio of reinforcements. The performance of the models was appraised by various statistical estimators and safety ratio, and compared with different theories for cracking torque and initial stiffness. Among all the calculation models, RF model achieved the best overall prediction performance with the highest coeffcient of determination (R2=0.985 for cracking torque and R2=0.978 for initial stifness) and lowest root-mean-square error (RMSE=5.867 for cracking torque and RMSE=3.994 for initial stiffness). However, theories for cracking torque, i.e., plastic theory, Bredt thin-tube theory and skew-bending theory, gave huge underestimation, whereas greatly exaggerated initial stiffness was obtained by elastic theory and simplified soften membrane model for torsion theory. Besides, input variable importance analysis was conducted, revealing that dimension parameters of cross-section were the most critical features to decide prediction performance for pre-cracking torsional performance of RC beams. The achievements of this paper may provide references to the establishment of new predicting model for pre-cracking torsional response of RC beams.

2

Influence of the percentage of reinforcement by un-stressed rebar on the deformability of pre-stressed RC beams

Blikharskyy Yaroslav, Selejdak Jacek, Bobalo Taras, Khmil Roman, Volynets Myhailo

Production Engineering Archives

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2021

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Vol. 27, Iss. 3

212--216

EN

This article presents the materials of deformability studies of pre-stressed steel-concrete beams reinforced with a package of reinforcement with different ratio of tape and rebar in the pure bending moment zone. The aim of the research was determination of the reinforcement percentage influence, for pre-stressed reinforced concrete beams reinforced with a package of reinforcement on their deformability. Also, the aim was to evaluate the effectiveness of using pre-stressed rebar in combined reinforcement. The practical significance of the experimental research is to study the deformability in pre-stressed bending elements with external tape and rebar reinforcement, taking into account the influence of different ratios of reinforcement areas within the combined reinforcement and development of proposals for such structures` calculation and design. The scientific novelty of the research is in obtaining the deformability characteristics of reinforced concrete beams reinforced with a package of reinforcement (tape and steel bars with periodic profile) with different ratios in the case of static loads` action.

3

Impact resistance of RC beams under different combinations of mass and velocity: mesoscale numerical analysis

Jin Liu, Lan Yuchang, Zhang Renbo, Du Xiuli

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 4

308--328

EN

The concrete structures under impact loading duress may be destroyed within an extremely short period of time. The importance and complexity of exploration on the impact resistance of concrete members make this area still open for discussion. In the present study, a 3-D mesoscale numerical model was established to investigate the effect of the combination of impact mass and velocity on the mechanical behavior of reinforced concrete (RC) beams subjected to impact loadings. Heterogeneity of concrete and strain rate effects of concrete and steel bars were taken into account. Furthermore, nonlinear interaction between the concrete and steel bars was considered herein. Results from macroscale and mesoscale simulation were compared with the available physical tests, indicating that the mesoscale numerical model can better represent the influence of heterogeneity of concrete on the mechanical behavior of RC beams. Five different impact energy levels were involved to study the effect of the combination of impact mass and velocity on the impact resistance of RC beams. At last, the residual bearing capacity and natural frequency of impacted RC beams were numerically calculated and their relationship was discussed. It is indicated that the deformation of RC beams is influenced strongly by the impulse, which increases with the increasing impact mass at identical impact energy. Besides, the failure mode of RC beams turns from shear-dominant failure mode to bending shear failure mode with the increase of impact mass, accompanied by the increase of energy dissipation of steel bars and the whole member. Despite this, in the present work, the combination of the impact mass and velocity had little influence on the damage extent (based on the performance) of the RC beams. Moreover, an empirical relationship between the residual bearing capacity and the natural frequency of the impacted RC beams was established as a rough reference for damage evaluation in engineering practice.

4

Comparison crack resistance of RC beams with and without transverse reinforcement after shear testing

Vegera Pavlo, Khmil Roman, Vashkevych Rostyslav, Blickharskyy Zinoviy

Quality Production Improvement - QPI

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2019

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Vol. 1, Iss. 1

342--349

EN

Main parameters, which characterize shear strength, are crack distribution, width of diagonal crack opening and angle of inclined crack. There are in this article, comparison crack resistant of testing reinforced concrete (RC) beams on the shear with such variable parameters like presence or absence internal reinforcement, different shear span, and presence or absence external composite reinforcement. Shear span (relative span to effective depth ratio) was acquired the following values: a/d=2, 1.5, 1. For internal reinforcement, rebar’s A240C with diameter 8 mm and steps 100 mm was chosen. The composite FRCM system was like external reinforcement with three stripe of composite fabric with width 70 mm and step 100 mm. Eight RC beams were tested. After testing, we discovered that the most influenced on the serviceability capacity was shear span. Internal transverse reinforcing increased shear strength on the same level and it was independent from shear span and other factors. Only quantity of reinforcing determine level of increasing shear capacity. FRCM system is efficient strengthening system, which significant increase shear crack resistant for RC beams. External FRCM reinforcing increase shear crack resistance on the same percentage and independent from presence or absence internal reinforcement.

5

Experimental verication of a numerical modelof RC beam with CFRP rope strengthening

Szczecina Michał, Tworzewski Paweł, Bacharz Kamil

Computer Assisted Methods in Engineering and Science

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2019

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vol. 26, no. 3-4

137-151

EN

This paper presents results of experimental tests and numerical analysis of reinforced concrete (RC)beams containing an additional carbon fibre rope strengthening. Two single-span RC beam specimenswith classical reinforcing bars and stirrups and one carbon fibre rope as near-surface mounted (NSM)strengthening were tested in a four-point bending test. The paper presents and compares the resultsregistered by the ARAMIS system during the test of two beams with carbon fibre rope under monotonicload with the results obtained in finite element analysis with Abaqus software using the concrete damagedplasticity model for concrete.

6

Analysis of the crack width of beams reinforced with FRP bars

Brózda K., Selejdak J., Koteš P.

Technical Transactions

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2018

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Vol. 115, iss. 11

163--168

EN

The paper investigates and compares a selected issue of Serviceability Limit State (SLS) of simply supported reinforced concrete (RC) beams subjected to various values of flexural stresses. Characteristic crack widths of beams reinforced with various types of bars were calculated. Beams reinforced with Glass Fiber Reinforced Polymer (GFRP), Carbon Fiber Reinforced Polymer (CFRP) and Aramid Fiber Reinforced Polymer (AFRP) were examined. The computational analysis of beams reinforced with FRP bars was based on Italian guideline for the design (CNR-DT 203/2006) and in accordance with the EC2 (EN 1992-11:2004). Based on the conducted analysis, the effect of changing the service live load on the increase in crack width was presented.

PL

W artykule omówiono i porównano wybrane zagadnienie Stanu Granicznego Użytkowalności (SLS) swobodnie podpartej jednoprzęsłowej zbrojonej belki betonowej, poddanej różnym wartościom naprężeń zginających. W celu przeprowadzenia analizy dokonano obliczeń szerokości rozwarcia rys prostopadłych do osi belek zbrojonych prętami kompozytowymi. Do obliczeń przyjęto pręty zbrojeniowe polimerowe wzmocnione włóknem szklanym (GFRP –Glass Fiber Reinforced Polymer), węglowym (CFRP – Carbon Fiber Reinforced Polymer) oraz aramidowym (AFRP – Aramid Fiber Reinforced Polymer). Obliczenia wytrzymałościowe belek zbrojonych prętami FRP (Fiber Reinforced Polymer) wykonano zgodnie z włoskimi zaleceniami projektowymi (CNR-DT 203/2006) oraz w oparciu o obowiązującą normę europejską Eurokod 2 (PN-EN 1992-1-1:2008). Na podstawie przeprowadzonej analizy przedstawiono wpływ zmiany obciążenia użytkowego na wzrost szerokości rozwarcia rysy.

7

Kierunki rozwoju badań płyt i belek żelbetowych

Samborski M.

Przegląd Budowlany

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2018

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R. 89, nr 12

50--55

PL

Wyczerpanie nośności na zginanie i ścinanie belek oraz płyt żelbetowych badane było głównie do lat 80. XX wieku. W tym okresie zwracano szczególną uwagę na charakter zarysowań elementów żelbetowych. W połowie XX wieku zapoczątkowano prace doświadczalne nad nowymi kierunkami badań. Programy badawcze dotyczyły głównie przebicia, a z czasem także działania wybuchu, pożaru lub stosowania nowatorskich materiałów w tym betonów wysokowartościowych lub wyrobów kompozytowych.

EN

Exhaustion of load-bearing capacity for bending and shearing of reinforced concrete beams and slabs was tested mainly up to the 1980. During this period, particular attention was paid to the nature of scratches of reinforced concrete elements. In the middle of the twentieth century, experimental work on new research directions was initiated. The research programs concerned mainly the breakthrough, and with time also the effects of explosion, fire or the use of innovative materials, including high-grade concretes or composite products.

8

Research of RC beams without stirrups and shear’s strengthening by FRCM system

Blikharskyy Z., Khmil R., Vegera P.

Zeszyty Naukowe Politechniki Częstochowskiej. Budownictwo

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2017

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Z. 23 (173)

16-25

EN

In this article shear strength of strengthened and non-strengthened reinforced concrete (RC) beams are described. The research program involves a one serie of test beams which contains control sample and three reinforced samples by reinforcing FRCM system. RC beams designed that the beams destruction after strengthening took place by shear. To accomplish it these beams were designed with a significant margin of tensile rebar. The maximum effect of increasing the shear strength (ULS) is 45% for samples strengthened without initial loading.

PL

W artykule opisano wytrzymałość na ścinanie wzmocnionych i niezbrojonych belek żelbetowych. Program badawczy obejmował jedną serię badawczą, w skład której wchodziła grupa belek kontrolnych i trzy grupy belek wzmocnionych z wykorzystaniem systemu FRCM. Belki żelbetowe zaprojektowano tak, że zniszczenie belek po wzmocnieniu nastąpiło przez ścinanie. Aby to osiągnąć, belki zostały zaprojektowane ze znacząco małą ilością zbrojenia podłużnego. Maksymalny efekt zwiększenia wytrzymałości na ścinanie (ULS) wynosi 45% dla próbek wzmocnionych bez początkowego obciążenia

9

Rozkład sił wewnętrznych w belkach żelbetowych bez zbrojenia na ścinanie

Bodzak P.

Czasopismo Inżynierii Lądowej, Środowiska i Architektury / Journal of Civil Engineering, Environment and Architecture

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2017

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z. 64, nr 3/I

325--332

PL

W artykule przedstawiono wyniki badań na ścinanie belek żelbetowych bez zbrojenia poprzecznego. Parametrem zmiennym była smukłość ścinania wynosząca odpowiednio 1,0; 1,5; 2,0 oraz 3,0. Badania pokazały, że pod wpływem ścinania następuje zmiana rozkładu sił wewnętrznych w strefie przypodporowej. Prowadzi to do zmniejszenia naprężeń ściskających w „ściskanej” części belki już we wstępnej w fazie formowania się krytycznej rysy ukośnej, która przecina oś zbrojenia w odległości d od podpory i jest to przekrój miarodajny do wymiarowania na ścinanie.

EN

The article presents comparison of experimental test results carried out on RC beams with different shear ratio and without shear reinforcement. According to this tests results in beams without transverse reinforcement the influence of shear is seen in the form of stress redistribution in the compression zone already before the diagonal cracking. This demonstrates in the form of stress reduction in the compression zone of the beam and in the subsequent load steps in the form of stretching and consequently cracking of “compression” part of the beam.

10

Wpływ granicy plastyczności zbrojenia głównego na nośność elementów wzmocnionych kompozytami CFRP

Bodzak P.

Budownictwo i Architektura

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2013

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Vol. 12, nr 1

85--90

PL

W artykule opisano badania elementów wzmocnionych taśmami CFRP, w których zastosowano róźne gatunki stali do wykonania zbrojenia podstawowego. Stwierdzono, iż zasadniczy wpływ na poziom siły niszczącej powodującej delaminację taśmy ma granica plastyczności zastosowanego zbrojenia.

EN

This paper describe tests on RC beams strengthened with externally bounded CFRP plates. A total of four PCC beams with rectangular 15×30cm cross section and 300cm clear span were manufactured and tested in four-point flexure with 100cm constant moment region. Low compressive strength of concrete fck about 20MPa and middle reinforcement ratio – 0,0075 were used. Different yield strengths of steel, from 360MPa to 1860MPa, were chosen as experimental variables. All the beams were strengthened with one CFRP strip measuring 5×1,2cm. The specimen failed at various load and at various ultimate strains of CFRP strips. It was generally observed that both the moment capacity and the ultimate strains grew with the increase of steel yielding strength. It could be deducted that in many cases reaching the yielding steel strength activates the deboning of FRP strips.

11

Research of reinforced-concrete beams deformations, renewed after the influence of aggressive environment

Blikharskiy Z., Khmil R., Vashkevych R.

Zeszyty Naukowe Politechniki Rzeszowskiej. Budownictwo i Inżynieria Środowiska

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2009

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z. 53 [265]

27-32

EN

The article presents the experimental and theoretical research of reinforced concrete beams deformations, damaged in the conditions of simultaneous influence of aggressive environment and loading with their further renewal. The peculiarity of this research is that during influence of aggressive environment reinforced-concrete beams were tested both under the action of loading and without it. The influence of aggressive environment and renewal took place in the conditions of the operating loading on the reinforced-concrete beams. Such a combination of influences allows to define the optimal method of research of the renewal process in reinforced-concrete structures and the influence of loading, at which the strengthening takes place on the efficiency of renewal and deformations of experimental samples. The experimental and theoretical values of deformations of reinforced-concrete beams which were renewed without loading and under the operating loading are obtained. Their comparison is carried out with the purpose of determining the optimal method of research of such structures.

12

Experimental investigation into behaviour of CFRP composite-strengthened RC beam under cyclic loading

Kmita A.

Archives of Civil and Mechanical Engineering

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2007

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Vol. 7, no 2

5-19

EN

This paper presents selected results of research on the behaviour of an RC beam strengthened with composite materials (CFRPs). The designed tests were to provide data for an assessment of such reinforcement system's performance under cyclically variable loads. The test plan incłuded the effect of the CFRP reinforcement on: beam rigidity, cracking morphology and the interaction ofthe reinforcement components with regard to bond uniformity in the whole structure and the durability of the bond under cyclic loads. The tests were carried out on two RC beams with the same dimensions, reinforcement and material quality. Only one of the beams was strengthened with CFRP, but both were subjected to the same loading and the same quantities were measured. This facilitated a quantitative and qualitative assessment of the performance of the CFRP reinforcement system. The research was carried out as part of project "Theoretical and experimental investigations of loadbearing capacity and service limit states of reinforced concrete and prestressed concrete structures" (also to be used for educational purposes) in the Accredited Laboratory of the Institute of Building Engineering at Wrocław University of Technology.

PL

W pracy przedstawiono wybrane wyniki badań nad zachowaniem się belki żelbetowej wzmocnionej materiałami kompozytowymi CFRP. Badania te zaprojektowano jako badania rozpoznawcze dla oceny skuteczności tego systemu wzmocnienia przy obciążeniach o charakterze cyklicznie zmiennym. W zrealizowanym programie badań ujęto takie zagadnienia jak: wpływ wzmocnienia na sztywność belek, na morfologię zarysowania i współpracę elementów wzmocnienia w aspekcie równomierności zespolenia w całym obszarze obiektu i trwałości tego zespolenia w czasie pod cyklicznymi obciążeniami. Badania przeprowadzono na dwóch belkach żelbetowych o takich samych wymiarach, zbrojeniu i jakości materiału. Jedna z tych belek została wzmocniona, ale obie zostały poddane jednakowemu procesowi obciążenia i pomiarowi tych samych wielkości. Ułatwiło to ocenę jakościową i ilościową skuteczności zastosowanego systemu wzmocnienia belek. Badania przeprowadzono w ramach zadania "Badania teoretyczne i doświadczalne stanów granicznych nośności i użytkowalności konstrukcji żelbetowych i sprężonych" (z wykorzystaniem do celów dydaktycznych) w Akredytowanym Laboratorium Instytutu Budownictwa Politechniki Wrocławskiej.