Crack Width Limit Research Articles

A case study on early-age cracking of high-strength concrete construction by coupled thermal-mechanical analysis and field monitoring

The use of high-strength concrete (HSC) in constructing high-rise reinforced concrete buildings and their deep foundations is becoming more popular because of the significant reduction in member size and, thus, self-weight in structural members. However, the higher cement content in HSC may result in increased heat of hydration and autogenous shrinkage, growing concerns about forming early-age cracks in HSC structural members. This case study assessed the early-age cracking of HSC in bored pile construction of high-rise buildings. A nonlinear transient coupled thermal-mechanical response analysis was performed to evaluate the potential of early-age cracking caused by the heat of hydration generated in the HSC using ABAQUS and two subprograms, USDFLD and UEXPAN. A 3-D finite element model was developed considering thermal effects, time-dependent evolution of early-age strength and stiffness of HSC, crack strain development, autogenous shrinkage, and stress-relaxation in the analysis. Field measurements were carried out on a 3-m diameter bored pile constructed using Grade C50/60 HSC (fck,cube = 60 MPa) for a high-rise building project in Hong Kong to evaluate the validity of the numerical model. Optical fiber sensors were used to monitor the temperature changes of the pile for approximately 380 hours after casting. The temporal and spatial temperature distributions measured in the field measurements agree well with the simulations. Large thermal gradients and high tensile stress zones were observed across the horizontal cross-sections of the pile, resulting in the formation of vertical annular cracks. Based on the results of the analysis, the maximum crack widths were predicted and compared with the durability crack width limits.

Model for rapid evaluation of corner crack widths in reinforced concrete dapped-end conections

Dapped-end connections are widely used in concrete infrastructure, and in particular in Gerber-type bridges and precast concrete buildings. The main vulnerability of such connections is the early opening of inclined cracks at the re-entrant corner of the dapped end. Such cracks are difficult to control as they propagate at low loads and open significantly before the occurrence of secondary cracks. The goal of this paper is to propose a rational model for rapid evaluation of the width of the corner cracks, including the effects of secondary cracking and, indirectly, the effect of restrained shrinkage at low loads. The model assumptions stem from detailed test observations of specimens with light and heavy reinforcement, arranged in orthogonal or diagonal layouts. The model is developed in two steps: 1) predicting the crack width at yielding of the connection, and 2) capturing the shape of the response from zero load up to yielding. A database of 42 tests with a broad range of variables is used to validate the model. It is shown that the main properties influencing the width of the corner crack are the amount and detailing of the reinforcement, and their effect is well captured by the model. It is also illustrated how the model can be used to design the reinforcement of dapped ends to meet crack width limits at service conditions.

A pre-failure narrow concrete cracks dataset for engineering structures damage classification and segmentation

Monitoring of structures’ condition plays a fundamental role in providing safety for users and extending the structures’ lifespan. The monitoring is conducted through on-site inspections by engineers thus this process is time-consuming, labor-intensive and prone to subjective engineering opinions. Detecting damage using machine learning algorithms on images can support engineers’ work, especially for early damages which are difficult to see with the human eye. This article is focused on the concrete crack detection problem in engineering structural elements. Despite the availability of several concrete crack detection datasets, no dataset allows semantic segmentation of cracks narrower than 0.3 mm (the crack width limit for typical engineering structures elements and environmental conditions according to EC 1992-1-1) and the ability for crack classification is limited. The provided open dataset represents only cracks below the crack width limit of 0.3mm, which do not yet indicate concrete elements failure. It is dedicated for early crack classification and segmentation, so that damage protection can be taken at an early stage to prevent structural element damages.

Experimental investigations on early crack development in fully restrained reinforced concrete members with active zero-displacement control

The development of restraint-induced stress in reinforced concrete members at an early age can be tested using setups applying either passive or active displacement control. To provide results relevant for the practical design of minimum reinforcement to limit the crack width, an actively controlled test setup for large specimens was developed to perform a systematic experimental campaign focusing on the early crack development under well-defined mechanical and thermal boundary conditions. The full degree of restraint achieved by actively preventing any displacement of the member allowed for the theoretical interpretation of early restraint-induced stress evolution, deformation behaviour in the cracked and uncracked regions, and reinforcement stress for a variety of parameters, including hydration rates, member height, bar diameters and subsequently reinforcement ratio. The cracking process, starting with primary cracks accompanied by secondary cracks within the effective reinforcement area, is monitored in combination with the development of the tensile strength and Young’s modulus of the concrete. Furthermore, the time of cracking and the forces released upon crack occurrence, considering the effect of self-equilibrating stresses, are determined, analysed, and compared with the results of crack-force based design rules to determine the minimum amount of reinforcement that ensures the crack width limitation.

Crack width, deflection, and strain limits of concrete beams with unstressed seven-wire steel strands as longitudinal reinforcement

ABSTRACT This study designed and tested six prototype beams longitudinally reinforced with either SD420 deformed steel bars, unstressed 1860-MPa seven-wire steel strands, or a combination of these. The experiment revealed that the displacement, crack width, and crack spacing increased with the increasing number of strands used to replace deformed bars as longitudinal reinforcement. Crack width was estimated using Frosch’s equation, which conservatively predicted the maximum crack width for beams with deformed bars and those with both strands and deformed bars; a modified version of the equation yielded more accurate values for the beams reinforced with strands only. A bond coefficient for strands was used in the modified equation. Strain limits for the tension- and compression-controlled sections of the beams with strands were determined to be 0.0145 and 0.0115, respectively. The deflection of the beams was well estimated using the ACI 318–19 equation.

Design method for bridge deck link slabs prepared using BFRP bar‐reinforced ecological high‐ductility cementitious composites by theoretical calculation and numerical simulation

AbstractBridge deck link slabs prepared using Basalt Fiber Reinforced Polymer (BFRP) bar‐reinforced ecological high‐ductility cementitious composites (Eco‐HDCC) were applied as substitutes for steel expansion joints in Malin Bridge. Theoretical calculations and numerical simulations were combined to develop a design method. The total length and debond length of the link slabs were assumed based on the bridge information, and the reinforcement ratio of the BFRP bar was calculated using the maximum crack width limit. Then, the flexural capacity of the link slabs was evaluated. A preliminary reinforcement program using eight reinforcement ratios and different bar diameters was developed. In addition, the maximum stresses, strains, and deflections of the link slabs were validated through Abaqus finite element analysis. The simulation results of the reinforcement programs with minor reinforcement ratios are similar. The maximum stresses, strains, and deflections of the link slab materials are significantly lower than the design ultimate capacities of the materials, implying that the eight reinforcement programs are feasible. Because the thickness of the link slabs is within the range of 80–120 mm, a small‐diameter bar is preferable. Furthermore, BFRP bars with diameters of 10–14 mm are suitable along the driving direction, whereas BFRP bars with diameters of 10 mm are recommended along the direction perpendicular to the driving direction. A detailed design method flowchart for bridge deck link slabs was constructed to serve as a guideline for engineers.

Durability Design of Concrete Structures Under Reinforce-ment Corrosion

Traditionally, the durability design of concrete structures is
 based on implicit rules (minimum concrete cover, maximum
 water/cement ratio, crack width limitation, etc.). The research on
 concrete durability during the last decades has produced a reliable
 basis for information on deterioration processes. Based on this
 knowledge, it is possible to start incorporating durability in the
 design of concrete structures. Standard reliability methods were
 used to evaluate time dependent reliability of concrete structures
 under corrosion attack.

Experimental and numerical study on the crack width and deflection performance of GFRP reinforced concrete beams

The design of glass fiber-reinforced polymer (GFRP) reinforced concrete (RC) members is often governed by the crack width and deflection serviceability limits due to the low elastic modulus of GFRP material compared to steel. The available formulations in the current standards and guidelines control the crack widths of the GFRP-RC elements by considering the bond interaction between the GFRP reinforcement and surrounding concrete through bond-dependent coefficient, kb. This study investigates the effect of different parameters, including the concrete compressive strength, clear concrete cover to GFRP reinforcement, and the number of GFRP reinforcement layers on the moment capacity, cracking progression, deflection behavior, and the variation of kb values at different crack widths. The study involves experimentally testing 11 full-scale GFRP-RC beams. Moreover, a numerical parametric model was developed to investigate the effect of varying the concrete strength on the deflection performance of the GFRP-RC beams. The experimental results provided insights into how the investigated parameters impact the crack width and deflection values at the service stage. Moreover, the numerical model simulated the experimental behavior of the beams with high accuracy. It was also found that the ACI 440.1R-15 deflection formulation underestimates the deflection values at the service stage, particularly at high concrete strengths.

Parametric Study to Decide the Optimal Rebar Grade for Flexural Members

The growing interest of using higher strength reinforcing steel for certain applications within the reinforced concrete industry is driven primarily by relief of congestion; particularly in buildings assigned a high seismic design category. Construction efficiency can be improved by high strength bar or combined with high strength concrete which allows reinforced concrete to be used in more demanding applications. High grade steel generally increases the cost as well allows smaller concrete member which creates a problem of placement of reinforcement. Therefore there is a need to study the better option between lower quantity of high grade and high quantity of lower grade. This paper presents the parametric study to see the effect of beam span and member sizes on the results obtained in design of simply supported flexural members using different rebar grades, such as Fe415, Fe500, Fe550 and Fe600 in terms of crack width and member deflections for mild and moderate exposure conditions. It was observed that detailing plays vital role in cost saving and crack width limit governs final steel requirement in moderate exposure condition. Cost analysis was also performed for different grades and Fe500 is found optimum grade.

FLEXURAL BEHAVIOR OF STEEL FIBER-REINFORCED LIGHTWEIGHT AGGREGATE CONCRETE BEAMS PRESTRESSED WITH CARBON FIBER-REINFORCED POLYMER BARS

An unbonded prestressing anchorage system for carbon fiber-reinforced polymer (CFRP) tendons was introduced. Eight lightweight aggregate concrete (LWC) beams prestressed with unbonded CFRP tendons which used CFRP auxiliary reinforcements and one fabricated using normal weight concrete (NWC) were tested under a four-point bending condition. The influences of concrete type, of prestressed degree and, of clear span length on the cracking moment, on the moment-deflection response and, on the crack width were analyzed. The existing deflection and crack width models for unbonded FRP prestressed beams with steel auxiliary reinforcements were modified from the view of equivalent axial stiffness. The applicability of the modified models was evaluated based on the test results. It is shown that the serviceability limit state of the beams is mainly governed by the crack width limit. The ratios between the moment at crack width of 0.5 mm and the ultimate moment range from 41% to 52%. With the same total reinforcement amount, the increase in the prestressed degree helps delay the cracking of the specimens. Increasing the amount of the auxiliary reinforcement and of the unbonded prestressed tendons both improve the beam stiffness and restrain the propagation of the cracks. The modified Cheng’s and modified Meng’s deflection models provide accurate deflection predictions for LWC beams with unbonded prestressed and auxiliary CFRP reinforcements.

Design method of serviceability limit states of BFRP bar reinforced ecological high ductility concrete beam: Experimental and theoretical analysis

Ecological high ductility concrete (Eco-HDC) has a larger tensile deformation than normal concrete, and Eco-HDC can be used to cast bridge deck link slab in negative moment zone. To acquire the flexural design method of bridge deck link slab made by BFRP (basalt fiber reinforced polymer) bar reinforced Eco-HDC, serviceability limit states of beam containing crack width and deflection are studied through the experimental and theoretical analysis. Test variables are diameter of BFRP bar, cover thickness and loading regime. Increasing the BFRP bar diameter or decreasing the cover thickness is an efficient method to decrease the maximum crack width. Cyclic loading type is also beneficial to reduce the maximum crack width. Besides, as the diameter increases, the peak deflection increases within a diameter of 8 mm ∼ 12 mm, and then decreases. Beam with a larger cover thickness has a lower peak deflection. Peak deflection is independent on the loading regime. Formulas in design codes are adopted to predict the maximum crack width and peak deflection, and the formulas are proposed to evaluate the test results. In addition, maximum crack width limit, maximum limit of stress and strain in Eco-HDC and BFRP bar are the governing parameters to compute the reinforcement ratio of BFRP bar in the design of bridge deck link slab.

Recent Advances in Strain-Hardening UHPC with Synthetic Fibers

This paper summarizes recent advances in strain-hardening ultra-high-performance concretes (UHPC) with synthetic fibers, with emphasis on their tensile properties. The composites described here usually contain about 2.0% high-density polyethylene (PE) fibers. Compared to UHPC with steel fibers, strain-hardening UHPC with synthetic fibers generally show a higher tensile ductility, lower modulus in the cracked state, and relatively lower compressive strength. The tensile strain capacity of strain-hardening UHPC with synthetic fibers increases with increasing tensile strength. The f’cftεt/w index (compressive strength × tensile strength × tensile strain capacity/tensile crack width) is used to compare the overall performance of strain-hardening UHPC. Moreover, a probabilistic approach is applied to model the crack width distributions of strain-hardening UHPC, and estimate the critical tensile strain in practical applications, given a specific crack width limit and cumulative probability. Recent development on strain-hardening UHPC with the use of seawater, sea-sand and PE fibers are also presented.

Serviceability performance of fiber-reinforced lightweight aggregate concrete beams with CFRP bars

Six lightweight aggregate concrete (LWC) beams reinforced with carbon fiber–reinforced polymer (CFRP) bars were tested under a four-point bending load with different steel fiber contents, reinforcement ratios, and clear span lengths to investigate their flexural behavior and serviceability performance. The test results showed that using steel fiber–reinforced lightweight aggregate concrete (SFLWC) and increasing the reinforcement ratio enhanced the serviceability performance of the beams. The incorporation of 0.6% by volume of steel fibers reduced the midspan deflection by 22.70%–36.87% at the same load level in service stage. At service load, all the CFRP-reinforced beams exhibited conservative deflections when compared to the deflection limits recommended by ACI 440.1 R and GB 50608, and satisfied the crack width limit of 0.7 mm. Comparing the measured maximum crack widths with the corresponding predictions revealed that the bond-dependent coefficient value of 1.4 specified in ACI 440.1 R was reasonable yet conservative. Moreover, an energy-based method was adopted to quantify the influence of the fibers on the beam stiffness. On this basis, a rational deflection model for SFLWC beams reinforced with CFRP bars was suggested.

CALCULATION METHOD FOR CRACK WIDTH OF STEEL FIBER-REINFORCED LIGHTWEIGHT AGGREGATE CONCRETE BEAMS REINFORCED WITH FRP BARS CONSIDERING BOND-SLIP BEHAVIOR

Regarding the crack development of concrete beams reinforced with fiber-reinforced polymer (FRP) bars as a process wherein the FRP bars are pulled out from concrete on both sides, a differential equation of crack width of lightweight aggregate concrete beams reinforced with FRP bars considering bond-slip behavior was established. According to the crack width limits provided by the design codes, the upper limit of slip was reasonably determined and constitutive models for bond-slip relationship between FRP bars and steel fiber reinforced-lightweight aggregate concrete in ‘low slip’ stage which were suitable to the service stage of the beams were proposed and introduced. The maximum crack spacing, lmax, amplification factor of crack width, h2/h1, and residual stress of fiber reinforced-concrete in cracked sections, σfib, were specified. On this basis, a crack width model of steel fiber reinforced-lightweight aggregate concrete beams reinforced with FRP bars was proposed using iterative algorithm and its accuracy was evaluated based on measured data of maximum crack width in service stage. It is shown that within crack width limit of 0.5 mm, the proposed model generates accurate maximum crack width predictions for steel fiber-reinforced lightweight aggregate concrete beams reinforced with FRP bars.

Applicability of Existing Crack Controlling Criteria for Structures with Large Concrete Cover Thickness

Abstract Widely used crack width calculation models and allowable crack width limits have changed from time to time and differ from region to region. It can be identified that some crack width calculation models consist with limitations for parameters like cover thickness. The current Norwegian requirement for cover thickness is larger than these limitations. The applicability of existing crack width calculation models and the allowable crack width limits must be verified for structures with large cover thickness. The background of crack width calculation models in Eurocode, Model Code 2010, Japanese code, American code and British code have been examined. By comparing the experimental crack widths with the predictions of the aforementioned models, the existing codes can be identified as requiring modification. Considering the durability aspect, it can be identified a long-term study proving that the allowable crack width can be increased with the increase in cover thickness. When considering the aesthetic aspect, the authors suggest categorizing the structures based on their prestige level and deciding the allowable crack widths accordingly. The paper proposes potential solutions for future research on how to improve both crack width calculation methods and allowable crack width limits to be used effectively in structures with large cover thickness.

Simplified Calculation Method of Wharf Bank Slope Stability Considering Old Piles

Based on the requirements of durability, a simplified calculation method of wharf slope stability considering the anti-sliding effect of old piles is derived according to the allowable cracks of old piles. Firstly, the acting force between the sliding soil and the pile is assumed to be distributed in a triangle, and the position of the resultant force of each pile is determined. According to the maximum crack width limit of the old pile, the maximum bending moment that the old pile can bear is calculated. According to the maximum bending moment, the maximum horizontal force at the mud surface, where is the slip arc position, can be inversely calculated, then the maximum anti-sliding force provided by the old piles can be obtained, and the stability of wharf bank slope considering the anti-sliding effect of the old piles is checked. In the slope stability calculation of Beira fishing wharf reconstruction project in Mozambique, the simplified calculation method considering the anti-sliding effect of old piles is adopted. The stability coefficient of wharf bank slope meets the requirements, and the extra treatment of bank slope is cancelled, which saves the project investment and construction period.

Seawater sea-sand engineered/strain-hardening cementitious composites (ECC/SHCC): Assessment and modeling of crack characteristics

Seawater sea-sand Engineered Cementitious Composites (SS-ECC) is a new version of ECC for marine constructions facing the scarcity of freshwater and river/manufactured sand. This study aims to assess and model the crack characteristics of SS-ECC, which are critical for its applications with non-corrosive reinforcements. The influence of sea-sand size, fiber length and fiber dosage on the crack characteristics of SS-ECC was explored. A five-dimensional representation was proposed to assess the overall performance of SS-ECC, by comprehensively considering both the crack characteristics (i.e., crack width and its variation) and the mechanical properties (i.e., compressive and tensile properties). A probabilistic model was also proposed to describe the stochastic nature and evolution of crack width, and it can be used to estimate the critical tensile strain on SS-ECC for a given crack-width limit and cumulative probability. The findings and proposed methods can facilitate the design of SS-ECC in marine and coastal structures.

Evaluation of Cracking and Serviceability Performance of Lightweight Aggregate Concrete Deep Beams

This paper investigated the diagonal crack propagation and serviceability performance of fifteen deep beams fabricated using lightweight aggregate concrete (LWAC). Experimental variables included the shear span-depth ratio, beam section depth, and bearing plate width. The test results were reported in terms of crack propagation, diagonal crack width, diagonal cracking load, and size effect on the serviceability of deep beams; they were also employed to establish a relationship between residual shear bearing capacity and maximum diagonal crack width for such components. In addition, the crack width limits in current code provisions were utilized to further evaluate the serviceability of LWAC deep beams. The test results revealed that the diagonal crack propagation is almost independent of the variation of beam depth, while the diagonal crack width exhibited an obvious increasing trend as shear span-depth ratio or bearing plate width increased. At service load level, the crack width limit of 0.4 mm stipulated in ACI 224-R-01 can be satisfied by LWAC deep beams with horizontal and vertical shear reinforcement ratios more than 0.3%.

Research on Anti-Crack Design of Super-Long Concrete Structure

There are many reasons for cracks at super-long concrete, which may be due to factors such as tensile stress and temperature shrinkage. Combined with the existing research and in-depth analysis from multiple angles, the causes of mass concrete cracks and the design method of temperature post-casting zone are described. Finally, related technical suggestions and supplementary measures were also put forward. At present, the anti-crack design of super-long concrete structures is mainly based on experience. Structural measures are used. The comprehensive effect lacks check and review. Even if the maximum crack width is checked, the load effect of concrete forming and cool shrinkage is basically not combined. For different requirements, an appropriate crack controlled standard is selected, and the maximum crack width limit of concrete specifications is generally used as the upper limit.

Bacteria-based self-healing concrete: evaluation of full scale demonstrator projects

Bacteria-based self-healing concrete is an innovative concrete that contains a self-healing agent that provides the material with enhanced autonomous crack-sealing performance. A specific type of this concrete, based on a healing agent composed of bacterial spores and lactate as carbon source, has been developed and applied by the Delft University of Technology for over ten years. Under laboratory conditions it was proven that, depending on the dosage of healing agent, self-healing of cracks up to 0.8 mm widths occurs. As such the material potentially allows reduction of steel reinforcement used for crack width limitation in watertight constructions. Application of self-healing concrete would therefore not only result in a reduction of costs but also in improvement of environmental performance (lower CO2 footprint) and ease of in situ casting due to reduction of use of steel in waterproof applications. However, according to the EN 1990 Eurocode (Basis of structural design), customary application of a novel type of concrete must be preceded by full scale demonstrators proving evidence for safe and functional performance. In this contribution we portray full scale application of bacteria-based self-healing agent as developed by the Delft research group in two repair mortar- and in two concrete construction demonstrator projects. These demonstrator projects show that addition of the bacteria-based self-healing agent to the concrete mix is safe as no negative side effects on construction performance was observed. However, it also proved difficult to find evidence for increased crack-healing performance as cracking in the demonstrator constructions hardly occurred. In further full scale demonstrators we therefore plan to drastically reduce amount of crack width-restraining reinforcement to show crack-healing capacity and potential to save on use of reinforcement steel in watertight concrete constructions.