Compressive Force Path Research Articles

Comparative Analysis of Shear Strength Prediction Models for Reinforced Concrete Slab–Column Connections

This research focuses on a comprehensive comparative analysis of shear strength prediction in slab–column connections, integrating machine learning, design codes, and finite element analysis (FEA). The existing empirical models lack the influencing parameters that decrease their prediction accuracy. In this paper, current design codes of American Concrete Institute 318-19 (ACI 318-19) and Eurocode 2 (EC2), as well as innovative approaches like the compressive force path method and machine learning models are employed to predict the punching shear strength using a comprehensive database of 610 samples. The database consists of seven key parameters including slab depth (ds), column dimension (cs), shear span ratio (av/d), yield strength of longitudinal steel (fy), longitudinal reinforcement ratio (ρl), ultimate load-carrying capacity (Vu), and concrete compressive strength (fc). Compared with the design codes and other machine learning models, the particle swarm optimization-based feedforward neural network (PSOFNN) performed the best predictions. PSOFNN predicted the punching shear of flat slab with maximum accuracy with R2 value of 99.37% and least MSE and MAE values of 0.0275% and 1.214%, respectively. The findings of the study are validated through FEA of slabs to confirm experimental results and machine learning predictions that showed excellent agreement with PSOFNN predictions. The research also provides insight into the application of metaheuristic models along with ANN, revealing that not all metaheuristic models can outperform ANN as usually perceived. The study also highlights superior predictive capabilities of EC2 over ACI 318-19 for punching shear values.

Knowledge-Based Prediction of Load-Carrying Capacity of RC Flat Slab through Neural Network and FEM

The present research work aims to compare the results for predicting the ultimate response of Reinforced Concrete (RC) members using Current Design Codes (CDCs), an alternative method based on the Compressive Force Path (CFP) method, and Artificial Neural Network (ANN). For this purpose, the database of 145 samples of RC Flat Slab with the simple supported condition under concentrated load is developed from the latest published work. All the cases studied were Square Concrete Slabs (SCS). The critical parameters used as input for the study were column dimension, cs, depth of the slab, ds, shear span ratio, a v s / d , longitudinal percentage steel ratio, ρls, yield strength of longitudinal steel, fyls, the compressive strength of concrete, fcs, and ultimate load-carrying capacity, Vus. Seven ANN models were trained using different combinations of input parameters and different points of hidden neurons with different activation functions. The results exhibited that SCS-4 was the most optimized ANN model, having the maximum value of R (89%) with the least values of MSE (0.62%) and MAE (6.2%). It did not only reduce the error but also predicted accurate results with the least quantity of input parameters. The predictions obtained from the studied models (i.e., CDCs, CFP, and ANN) exhibited that results obtained using the ANNs model correlated well with the experimental data. Furthermore, the FEM results for the selected cases show the closer result to the ANN predictions.

Sustainable Reinforced Concrete Design of Structural Walls

Sustainability calls for reduction in the use of natural resources and man-made materials. In light of this, the present study demonstrates the potentials of the reduction of transverse reinforcement in structural walls. A structural wall 1.7 m long was designed following the Greek Code for Reinforced Concrete (GCRC). This wall was then constructed and tested under cyclic loading. The theoretical value of the uncracked stiffness was four times greater than the value calculated after the experiment. The wall was also designed according to the Compressive Force Path method (CFP), which allowed for a significant reduction in the transverse reinforcement for the same target values.

Neural Network-Based Prediction: The Case of Reinforced Concrete Members under Simple and Complex Loading

The objective of this study is to compare conventional models used for estimating the load carrying capacity of reinforced concrete (RC) members, i.e., Current Design Codes (CDCs), with the method based on different assumptions, i.e., the Compressive Force Path (CFP) method and a non-conventional problem solver, i.e., an Artificial Neural Network (ANN). For this purpose, four different databases with the details of the critical parameters of (i) RC beams in simply supported conditions without transverse steel or stirrups (BWOS) and RC beams in simply supported conditions with transverse steel or stirrups (BWS), (ii) RC columns with cantilever-supported conditions (CWA), (iii) RC T-beams in simply supported conditions without transverse steel or stirrups (TBWOS) and RC T-beams in simply supported conditions with transverse steel or stirrups (TBWS) and (iv) RC flat slabs in simply supported conditions under a punching load (SCS) are developed based on the data from available experimental studies. These databases obtained from the published experimental studies helped us to estimate the member response at the ultimate limit-state (ULS). The results show that the predictions of the CFP and the ANNs often correlate closer to the experimental data as compared to the CDCs.

Beam theory – a proposed alternative basis for RC design

It has recently been shown that the ever-increasing complexity and inability of methods used for the design of reinforced concrete (RC) structures to consistently safeguard against brittle types of failure is the outcome of the conflict between the assumptions of the underlying theory and the fundamental concrete material characteristics. This paper demonstrates that these drawbacks can be eliminated through a coherent alternative theory developed on the basis of simplified beam theory modified to account for true concrete behaviour. Through the use of experimental information obtained from the literature, the proposed theory shows that, in contrast with widely held views, a structural member's load-carrying capacity depends solely on the strength of the compressive zone, which was found to be significantly larger than what it is widely considered to be. Moreover, load transfer is accomplished by the bending action of the concrete cantilevers formed between consecutive inclined or flexural cracks in the tensile zone. The above findings essentially underline the development of an alternative design method – the compressive force path method – and this is an indication of the suitability of the proposed theory to open up new possibilities for improving RC design.

Reliability analysis of models for predicting T-beam response at ultimate limit response

The aim of the present paper is to compare the current design codes’ predictions for reinforced concrete (RC) T-beams with the alternative physical methods – namely, the compressive force path (CFP) method and artificial neural networks (ANNs). Therefore, two databases, for T-beams without stirrups and with stirrups, are developed using the available experimental studies. The comparative study on prediction (obtained from the American Concrete Institute and Eurocode 2, CFP and ANN models) shows that the predictions of the ANN model provide a closer fit to the experimental results; after ANN the predictions of the CFP method are close to the experimental results when compared with the counterpart physical model. Comparative studies are also conducted on the critical parameters for the behaviour of RC T-beams. Furthermore, a non-linear finite-element tool (i.e. Abaqus) is used to validate the prediction of the ANN and CFP model. The crack pattern from Abaqus exhibited the same mechanics, on which the CFP models are based.

Assessing the accuracy of RC design code predictions through the use of artificial neural networks

In light of recently published work highlighting the incompatibility between the concepts underlying current code specifications and fundamental concrete properties, the work presented herein focuses on assessing the ability of the methods adopted by some of the most widely used codes of practice for the design of reinforced concrete structures to provide predictions concerning load-carrying capacity in agreement with their experimentally established counterparts. A comparative study is carried out between the available experimental data and the predictions obtained from (1) the design codes considered, (2) a published alternative method (the compressive force path method), the development of which is based on assumptions different (if not contradictory) to those adopted by the available design codes, as well as (3) artificial neural networks that have been calibrated based on the available test data (the later data are presented herein in the form of a database). The comparative study reveals that the predictions of the artificial neural networks provide a close fit to the available experimental data. In addition, the predictions of the alternative assessment method are often closer to the available test data compared to their counterparts provided by the design codes considered. This highlights the urgent need to re-assess the assumptions upon which the development of the design codes is based and identify the reasons that trigger the observed divergence between their predictions and the experimentally established values. Finally, it is demonstrated that reducing the incompatibility between the concepts underlying the development of the design methods and the fundamental material properties of concrete improves the effectiveness of these methods to a degree that calibration may eventually become unnecessary.

Shear failure criterion for RC T-beams

The paper is concerned with the development of a failure criterion capable of accurately predicting the shear capacity of reinforced concrete T-beams while correctly accounting for the beneficial effect of the increase of the compressive zone due to the presence of flanges. The development of the subject criterion is based on an alternative design method (the compressive force path method) that leads to predictions of reinforced concrete structural behaviour and design solutions considerably different compared to those of the current design codes without however compromising structural performance requirements (mainly associated with ductility and strength). The validity of the proposed failure criterion is verified through a comparative study of the calculated values with their experimentally-established counterparts obtained from an extensive literature survey. Through this comparative study it is demonstrated that the predictions of the proposed criterion provide a closer fit to the available experimental data than their counterparts obtained from the design codes considered.

Behavioral Study of RC Beams Designed for Shear Using CFP and ACI Code Models

Compressive Force Path concept is a proposed shear design method to explain shear behavior in reinforced concrete beams. This concept identifies 04 behaviors based on the shear span to beam depth (a/d) ratio and provides detailed shear design and transverse reinforcement detailing procedure for each behavior. Therefore, author of this paper intended to use this concept as a practical tool for the designing of RC beams particularly for Type II (2 ≤ a/d < 5) and Type III (1 < a/d < 2) behaviors to validate the concept. Total 08 beams of 100×200×1800 mm size beams were cast; out of which, 04 beams were designed according to ACI Code approach while, rest were designed and detailed using CFP concept strategy. The beam sizes in this study are identical and all parameters are constant except shear span 'a'. The two-point loading test results of RC beams showed that the shear resistance of concrete is better estimated by the CFP concept with a good prediction of cracks pattern, load carrying capacity and actual behavior of the beams in shear as compared to the beams designed according to ACI Code approach. However, most of the beams, particularly a/d ratio less than 4.44 were observed to be deficient in serviceability and failed in shear in spite of attaining theoretical predicted loads.

Design for earthquake-resistant short RC structural walls

The application of the compressive force path method for the design of earthquake-resistant reinforced concrete structural walls with a shear span-to-depth ratio larger than 2.5 has been shown by experiment to lead to a significant reduction of the code specified transverse reinforcement within the critical lengths without compromising the code requirements for structural performance. The present work complements these findings with experimental results obtained from tests on structural walls with a shear span-to-depth ratio smaller than 2.5. The results show that the compressive force path method is capable of safeguarding the code performance requirements without the need of transverse reinforcement confining concrete within the critical lengths. Moreover, it is shown that ductility can be considerably increased by improving the strength of the two bottom edges of the walls through the use of structural steel elements extending to a small distance of the order of 100 mm from the wall base.

Design for earthquake-resistent reinforced concrete structural walls

The work presented is concerned with the application of the compressive force path (CFP) method for the design of earthquake resistant reinforced concrete structural walls. It is based on a comparative study of the results obtained from tests on structural walls under cyclic loading mimicking seismic action. Of the walls tested, half have been designed in accordance with the CFP method and the remainder in accordance with the provisions of euro-codes 2 and 8. The results obtained show that both methods of design adopted lead to solutions which satisfy the requirements of current codes for structural performance in all cases investigated. Moreover, the solutions obtained from the application of the CFP method result in a significant reduction of the amount of stirrup reinforcement placed at the critical lengths of the walls’ vertical edges. In fact, such reinforcement is not specified by the latter method for the case of walls with a span-to-depth ratio smaller than 2.5; for the case of walls with a shear span-to-depth ratio larger than 2.5, not only is it placed over a length which is considerably smaller, but also its spacing is significantly larger, than the code specified values.

Effect of axial compression on shear capacity of linear RC members without transverse reinforcement

Failure criteria are proposed that allow for the effect of axial compression on the load-carrying capacity of linear reinforced concrete (RC) structural elements, without transverse reinforcement, exhibiting non-flexural modes of failure. These criteria are presented in a simple form expressing the causes of brittle failure, as described by the compressive force path theory, without the need of calibration through the use of experimental data. The validity of the proposed criteria is verified through a comparative study of their predictions with the values calculated from code-adopted formulae and experimental values obtained from the literature for the whole range of values of axial compression encountered in practical structural design.

Effect of transverse reinforcement on short structural wall behaviour

This paper reports on an investigation of the effect of the transverse reinforcement arrangement on the effective ductility of short structural walls. The work described is based on a comparative study of the behaviour of three pairs of specimens, with different transverse reinforcement arrangements, tested under cyclic loading. Two of the reinforcement arrangements investigated are those specified by Eurocode 8 (EC8) for medium and high ductility levels and the third is that resulting from application of the compressive force path method, with the latter method, unlike EC8, not specifying confining reinforcement within the critical regions. The results obtained indicate that, in spite of the significant differences in the reinforcement arrangement, all specimens exhibited similar behaviour as regards ductility, load-carrying capacity and mode of failure, the latter being characterised by crushing of concrete and buckling of the flexural bars within the compressive zone at the base of the specimens.

An appraisal of dowel action in reinforced concrete beams

The purported mechanism of dowel action in the shear capacity of longitudinally reinforced concrete beams has been revisited, and the results of an experimental investigation of the effect of bar size and amount of tension reinforcement on the load-carrying capacity of such beams designed to fail in shear are discussed. Both the test results, as well as an analysis using the compressive-force path concept, indicate that, for a given grade of steel and concrete, cover and the amount of tension reinforcement, the bar diameter has an insignificant effect on load-carrying capacity, which implies that dowel action is unlikely to be a significant mechanism in the shear capacity of longitudinally reinforced concrete beams. The observed nominal increase in shear strength of the beams with higher amounts of tension reinforcement is attributed to the better control of flexural cracking associated with larger steel ratios, which can increase the component of aggregate interlock in the shear transferred across inclined cracks.

An appraisal of the compressive force path concept

The results of an experimental appraisal of the compressive force path concept are presented in the form of a comparative study of the behaviour of beams reinforced in compliance with this concept and that of beams designed for shear in compliance with codal provisions based on the 45° truss analogy. The experimental results support the assertion of the compressive force path concept that the causes of failure of shear critical beams are associated with stress conditions in the region of the path along which the compressive chord force is transmitted to the supports and not with the traditional concept of shear capacity of a critical section. The experiments confirmed that although detailing of transverse reinforcement in the shear span of a beam following the recommendations of the 45° truss analogy will prevent a premature shear failure, such detailing in itself may not be sufficient to provide appreciable ductility to the member. Significant enhancement of ductility was observed in those beams in which the transverse reinforcement had been extended from the shear span into the flexure span in compliance with the compressive force path concept.

Reducing Steel Congestion without Violating Seismic Performance Requirements

This paper is concerned with an experimental investigation of the behavior of reinforced concrete (RC) beam-column specimens subjected to cyclic loading combined with a constant axial force. The specimens have the same geometry and longitudinal reinforcement but differ, on one hand, in that the portion of the longitudinal reinforcement within the critical regions is debonded from concrete in certain specimens and, on the other hand, in the transverse reinforcement arrangement; the latter is designed either in compliance with the earthquake-resistant design clauses of the current European codes or in accordance with the method of the compressive force path. The results obtained indicate that adopting the latter method yields significantly less transverse reinforcement in the critical regions without compromising the code performance requirements. Moreover, when the application of this method is combined with debonding the longitudinal reinforcement within these regions from concrete, a significant improvement in structural behavior is achieved.

Seismic behaviour of RC walls: an attempt to reduce reinforcement congestion

The paper is concerned with an experimental investigation of the behaviour of two types of structural concrete walls, which are subjected to static monotonic and cyclic loading and have the same geometry and vertical reinforcement details but differ in the horizontal reinforcement arrangement – the latter designed either in compliance with the earthquake-resistant design clauses of the current European codes or in accordance with the method of the compressive force path. It is intended to verify the findings of previous analytical work on the subject which has shown that adopting the latter method yields significantly more efficient design solutions without compromising the code performance requirements.

Seismic design of structural concrete walls: an attempt to reduce reinforcement congestion

Non-linear finite-element analysis is used for a comparative study of the behaviour of two types of structural concrete walls: walls W1 with a value of the shear span-to-depth ratio between 1 and 2; and walls W2 with a value of the above ratio larger than 2. The walls, which are subjected to static (monotonic and cyclic) and dynamic (seismic excitation) loading, have the same geometry and vertical reinforcement details but differ in the horizontal reinforcement arrangement, the latter designed either in compliance with the earthquake-resistant design clauses of current codes or in accordance with the method of the compressive force path. The results obtained indicate that adopting the latter method yields significantly more efficient design solutions without compromising the code performance requirements.

Earthquake-resistant design of indeterminate reinforced-concrete slender column elements

The work extends the range of application of previous work, which had been concerned with the earthquake-resistant design of reinforced concrete short column elements (elements with a shear span-to-depth ratio smaller than 2), by means of an experimental investigation into the behaviour of slender column elements (elements with a shear span-to-depth ratio larger than 2). As for the previous study, the present investigation of slender column elements is based on the use of indeterminate specimens (which represent more realistically elements in a building than their determinate counterparts) designed by using two different methods: the truss analogy method, as applied by current codes of practice, and the compressive-force path method. The results obtained indicated that the unexpected, premature brittle mode of failure observed in short column elements in the region of the point of inflection also characterises slender column elements when designed to current code provisions. In contrast, those elements designed to the compressive-force path method are found to satisfy the performance requirements of current codes for both strength and ductility.

A new methodology for repairing and strengthening RC members in seismic regions

The work described in this paper is concerned with the application of the method of the compressive force path (CFP) to the strengthening of reinforced concrete (RC) structures designed for seismic action (the initial design of the member(s) covers both CFP design and design to current Eurocodes). Carbon fibre-reinforced polymer sheets are used for this purpose. Eight column specimens were tested under the combined action of a constant axial force and monotonic or cyclic lateral displacement. The eight columns were tested in groups of two, each group having one specimen strengthened initially and then tested to failure, while the second specimen was tested without strengthening, and was repaired and strengthened before testing it to failure. The tests showed that the strengthening procedure based on the CFP fully satisfied the performance requirements of current code provisions for strength and ductility irrespective of whether the initial design followed Eurocodes or the CFP methodology. Moreover, all strengthened (or repaired and strengthened) specimens had stiffnesses similar to those of their virgin counterparts.