Assessment of shear capacity of adhesive anchors for structures using neural network based model

In this study, an artificial neural network (NN) based explicit formulation for predicting the edge breakout shear capacity of single adhesive anchors post-installed into concrete member was proposed. To this aim, a comprehensive experimental database of 98 specimens tested in shear was used to train and test NN model as well as to assess the accuracy of the existing equations given by American Concrete Institute and prestressed/precast concrete Institute. Moreover, the proposed NN model was compared with another existing model which had been derived from gene expression programming by the authors in a previous study. The prediction parameters utilized for derivation of the model were anchor diameter, type of anchor, edge distance, embedment depth, clear clearance of the anchor, type of chemical adhesive, method of injection of the chemical, and compressive strength of the concrete. The proposed model yielded correlation coefficients of 0.983 and 0.984 for training and testing data sets, respectively. It was found that the predictions obtained from NN agreed well with experimental observations, yielding approximately 5 % mean absolute percent error. Moreover, in comparison to the existing models, the proposed NN model had all of the predicted values in ±20 % error bands while the others estimated up to %160 error

A novel formulation of the flexural overstrength factor for steel beams

The ductile design of steel structures is directly influenced by the flexural behaviour of steel beams,which should be sufficient to allowplastic hinges to rotate until the collapsemechanismis completely developed. To guarantee the achievement of such a performance, the beam flexural overstrength must be quantified to appropriately apply capacity design principles. To this aim, analytical formulations to predict the flexural overstrength factor (s) of steel beams with a wide range of cross-section typologies (I and H sections, square and rectangular hollow sections) were developed based on gene expression programming (GEP). An experimental database was gathered from the available literature and processed to obtain the training and testing databases for the derivation of the closed-form solution through GEP. The independent variables used for the development of the prediction models were the geometric properties of the sections, the mechanical properties of the material, and the shear length of the steel beams. The predictions of the proposed GEP-based models were compared with the results obtained using the existing analytical equations proposed in the current literature. Comparative analysis revealed that the proposed formulation provides a more accurate prediction of beam overstrength

Characterization of rubberized cement bound aggregate mixtures using indirect tensile testing and fractal analysis

The main focus of this paper is to investigate the tensile properties of virgin and rubberized cement bound granular mixtures. This was conducted using indirect tensile testing with lateral displacement measurements, nondestructive resonant frequency testing, X-ray CT and quantitative assessment for cracking pattern using fractal analysis. The investigated properties were density, compacity, indirect tensile strength (ITS), indirect tensile static modulus, toughness, dynamic modulus of elasticity, dynamic modulus of rigidity, dynamic poison’s ratio, fractal dimension and fracture energy. To keep the same aggregate packing, the natural aggregate was replaced by waste tyres’ crumb rubber of similar gradation. Four volumetric replacement percentages (0%, 15%, 30% and 45%) of the 6 mm fraction size were utilized. This adjustment was observed to affect the material density not only due to the lower specific gravity, but because it also affects the compactibility of the mixture negatively due to the damping action of the rubber particles. In addition, strength was also affected detrimentally. However, material toughness was improved and stiffness was mitigated. The latter findings were supported by quantitative assessment of the cracking pattern which revealed more tortuosity and a higher fractal dimension as a result of rubber content increasing. A failure mechanism for this type of mixture was suggested and support by examining the internal structure of failed samples using X-ray CT. Overall, construction of cement-stabilized aggregate base with a small percentage of added crumb rubber may ensure a more sustainable and environmental-friendly pavement material and, at the same time, improve the properties of stabilized layers. However, behaviour of these mixtures under cyclic loading and evaluation of their durability should be assessed to fully validate their use

Strength and durability of composite concretes using municipal wastes

The influence of different types of polyethylene (PE) substitutions as partial aggregate replacement of micro-steel fiber reinforced self-consolidating concrete (SCC) incorporating incinerator fly ash was investigated. The study focuses on the workability and hardened properties including mechanical, permeability properties, sulfate resistance and microstructure. Regardless of the polyethylene type, PE substitutions slightly decreased the compressive and flexural strength of SSC initially, however, the difference was compensated at later ages. SEM analysis of the interfacial transition zone showed that there was chemical interaction between PE and the matrix. Although PE substitutions increased the permeable porosity and sorptivity, it significantly improved the sulfate resistance of SCC. The influence of PE shape and size on workability and strength was found to be more important than its type. When considering the disposal of PE wastes and saving embodied energy, consuming recycled PE as partial aggregate replacement was more advantageous over virgin PE aggregate replaced concrete

Strength, stiffness and ductility of concrete-filled steel columns under axial compression

YesExtensive experimental and theoretical studies have been conducted on the compressive strength of concrete-filled steel tubular (CFST) columns, but little attention has been paid to their compressive stiffness and deformation capacity. Despite this, strength prediction approaches in existing design codes still have various limitations. A finite element model, which was previously proposed by the authors and verified using a large amount of experimental data, is used in this paper to generate simulation data covering a wide range of parameters for circular and rectangular CFST stub columns under axial compression. Regression analysis is conducted to propose simplified models to predict the compressive strength, the compressive stiffness, and the compressive strain corresponding to the compressive strength (ductility) for the composite columns. Based on the new strength prediction model, the capacity reduction factors for the steel and concrete materials are recalibrated to achieve a target reliability index of 3.04 when considering resistance effect only

Optimisation of rubberised concrete with high rubber content: an experimental investigation

This article investigates experimentally the behaviour of rubberised concrete (RuC) with high rubber content so as to fully utilise the mechanical properties of vulcanised rubber. The fresh properties and short-term uniaxial compressive strength of 40 rubberised concrete mixes were assessed. The parameters examined included the volume (0–100%) and type of mineral aggregate replacement (fine or coarse), water or admixture contents, type of binder, rubber particle properties, and rubber surface pre-treatments. Microstructural analysis using a Scanning Electron Microscope (SEM) was used to investigate bond between rubber and concrete at the Interface Transition Zone (ITZ). This initial study led to the development of an “optimum” RuC mix, comprising mix parameters leading to the highest workability and strength at all rubber contents. Compared to a non-optimised concrete with 100% replacement of fine aggregates with rubber, the compressive strength of concrete with optimised binder material and moderate water/binder ratio was enhanced by up to 160% and the workability was improved significantly. The optimisation proposed in this study will lead to workable high rubber content RuC suitable for sustainable high-value applications

Flexural characteristics of rubberized cement-stabilized crushed aggregate for pavement structure

The purpose of this paper is to investigate the flexural characteristics and to quantitatively study the flexural-induced cracking of reference and rubberized cement stabilized aggregate mixtures. Four volumetric replacement percentages (0%, 15%, 30% and 45%) of 6 mm fraction size were used. This modification was found to affect the material strength detrimentally. However, material toughness was improved and stiffness was reduced. The latter findings were supported by quantitative assessment of the fractured surfaces which revealed more tortuous and rougher cracking as a result of rubber content increasing. This, in turn, may ensure a good load transfer across the cracks after their formation. Overall, using rubber in pavement construction is a sustainable solution that ensures consumption of large quantities of these waste materials. At the same time, it may be considered as a promising method to reduce cracking tendency and sensitivity which may improve shrinkage, thermal and fatigue performance

The use of electrical impedance spectroscopy for monitoring the hydration products of Portland cement mortars with high percentage of pozzolans

In this paper, mortars and pastes containing large replacement of pozzolan were studied by mechanical strength, thermogravimetric analysis (TGA), scanning electronic microscopy (SEM), mercury intrusion porosimetry (MIP) and electrical impedance spectroscopy (EIS). The effect of metakaolin (35%) and fly ash (60%) was evaluated and compared with an inert mineral addition (andalusite). The portlandite content was measured, finding that the pozzolanic reaction produced cementing systems with all portlandite fixed. The EIS measurements were analyzed by the equivalent electrical circuit (EEC) method. An EEC with three branches in parallel was applied. The dc resistance was related to the degree of hydration and allowed us to characterize plain and blended mortars. A constant phase element (CPE) quantified the electrical properties of the hydration products located in the solid¿solution interface and was useful to distinguish the role of inert and pozzolanic admixtures present in the cement matrix.The authors thank the Universitat Politecnica de Valencia (UPV, Vicerrectorado de Investigacion) for its support (project PAID-05-09 ref 4302) and Debra Westall (UPV) for revising the manuscript.Cruz González, JM.; Fita Fernández, IC.; Soriano Martinez, L.; Paya Bernabeu, JJ.; Borrachero Rosado, MV. (2013). The use of electrical impedance spectroscopy for monitoring the hydration products of Portland cement mortars with high percentage of pozzolans. Cement and Concrete Research. 50:51-61. doi:10.1016/j.cemconres.2013.03.019S51615