Effects Of Concrete Cracking Research Articles

Effect of concrete cracks on dynamic characteristics of powerhouse for giant-scale hydrostation

With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse. Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits. Results in this paper have been verified by practice of Three-Gorge Project.

Sustainable urban development and geophysics

Sustainable urban development and geophysics

An analytical-numerical procedure for cracking and time-dependent effects in continuous composite beams under service load

An analytical-numerical procedure has been presented in this paper to take into account the non-linear effects of concrete cracking and time-dependent effects of creep and shrinkage in the concrete portion of the continuous composite beams under service load. The procedure is analytical at the element level and numerical at the structural level. The cracked span length beam element consisting of uncracked zone in middle and cracked zones near the ends has been proposed to reduce the computational effort. The progressive nature of cracking of concrete has been taken into account by division of the time into a number of time intervals. Closed form expressions for stiffness matrix, load vector, crack lengths and mid-span deflection of the beam element have been presented in order to reduce the computational effort and book-keeping. The procedure has been validated by comparison with the experimental and analytical results reported elsewhere and with FEM. The procedure can be readily extended for the analysis of composite building frames where saving in computational effort would be very considerable.

Hybrid Procedure for Cracking and Time-Dependent Effects in Composite Frames at Service Load

A hybrid analytical-numerical procedure has been presented to take into account the effect of concrete cracking and time-dependent effects of creep and shrinkage in composite beams of the composite frames subjected to service load. The procedure is analytical at the element level and numerical at the structural level. The cracked span length beam element consisting of an uncracked zone in middle and cracked zones at the ends has been proposed for the composite beams to reduce the computational effort. The progressive nature of cracking of concrete of composite beams has been taken into account by division of the time into a number of time intervals. Closed form expressions for flexibility coefficients, end displacements, crack lengths, and midspan deflection of the cracked span length beam element have been presented in order to reduce the computational effort. The procedure has been validated in a limiting case by comparison with the experimental and analytical results reported elsewhere and also by comparison with FEM. The proposed procedure would lead to a considerable saving in computational time in case of large composite structures, e.g., tall composite building frames.

Nonlinear Stiffness Design Optimization of Tall Reinforced Concrete Buildings under Service Loads

Tall reinforced concrete (RC) building designs must satisfy serviceability stiffness criteria in terms of maximum lateral displacement and interstory drift. It is therefore important to assess accurately the effects of concrete cracking on lateral stiffness of such structures. This study integrates nonlinear cracking analysis methods with a powerful optimization technique and presents an effective numerical approach for the stiffness-based optimum design of tall RC buildings under service loads. A probability-based effective stiffness method is employed to identify cracked members and to modify their effective cracked stiffness. Iterative procedures are necessary for the serviceability analysis of tall RC buildings to determine their nonlinear stiffness characteristics due to concrete cracking. Design optimization based on a rigorously derived optimality criteria approach involves minimizing the cost of RC structures while satisfying the top and multiple interstory drift constraints along with member sizing requirements. A framework example is presented to illustrate the applicability and efficiency of this proposed optimal design tool. Discussions about the effects of concrete cracking on the optimization results are also included.

Optimal drift design of tall reinforced concrete buildings with non-linear cracking effects

This paper presents an efficient, computer-based technique for the optimum drift design of tall reinforced concrete (RC) buildings including non-linear cracking effects under service loads. The optimization process consists of two complementary parts: an iterative procedure for the non-linear analysis of tall RC buildings and a numerical optimality criteria (OC) algorithm. The non-linear response of tall RC buildings due to the effects of concrete cracking is obtained by a series of linear analyses, the so-called direct effective stiffness method. In each linear analysis, cracked structural members are first identified and their stiffness modified based on a probability-based effective stiffness relationship. Stiffness reduction coefficients are introduced as measures of the remaining stiffness for structural elements after cracking. A rigorously derived OC method is developed to solve for the minimum weight/cost design problem subject to multiple drift constraints and member sizing requirements. A shear wall-frame example is presented to illustrate the application of this optimal design method. The design results of the optimized structure with cracking effects are compared to those of the linear-elastic structure without concrete cracking. Copyright © 2005 John Wiley & Sons, Ltd.

Inelastic Dynamic Behavior of Hybrid Coupled Walls

This paper presents an investigation of the seismic behavior of hybrid coupled wall systems, in which steel beams are used to couple reinforced concrete shear walls. System response is studied using transient finite element analyses that account for the effect of concrete cracking, crushing, and steel yielding. Shear stresses in the concrete constitutive model are handled separately from normal stresses, which allows concrete to undergo high shear deformations without causing premature concrete crushing in the model. The developed finite element models are validated through comparisons with more refined models and test data. Suites of analyses are conducted to investigate pertinent parameters including hazard level, earthquake record scaling, dynamic base shear magnification, interstory drift, shear distortion, coupling beam plastic rotation, and wall rotation. The analyses show that hybrid coupled walls are particularly well suited for use in regions of high seismic risk.

Sleeve-type expansion anchor behavior in cracked and uncracked concrete

A test was performed to investigate the effect of concrete cracks on the static behavior of sleeve-type expansion anchors, and to confirm the seismic and fatigue resistance capability in cracked concrete. The tensile and shear test was conducted on single anchors with three different anchor diameters. Concrete test specimens are sufficiently large to prevent the effect of the concrete edges on the anchor behavior. The types of failure, the static strength and displacement behavior of the anchors in uncracked and cracked concrete were compared to evaluate the effect of the cracks. The strength reduction rate of the anchors due to the cracks was exhibited almost less than the corresponding value specified in ACI 349-01, APP. B. Through the residual strength tests, the seismic and fatigue resistance capability of the anchors was confirmed in cracked concrete. The characteristics of the anchor shear capacity significantly vary with how the displacement failure criteria are determined.

Nonlinear seismic response of reinforced‐concrete free‐standing towers with application to TV towers on flexible foundations

AbstractReinforced‐concrete (R/C) free‐standing towers such as TV towers are often analysed using elastic analyses as fixed‐base cantilever beams, ignoring the effect of soil–structure interaction. To take the capacity of structures after yielding into account, most designers usually prefer to decrease the peak values of the elastic response spectrum for the maximum credible earthquake (MCE) anticipated at the site by a factor called the ductility capacity factor, which varies with the design earthquake level and the structural characteristics of the structure neglecting the effect of supporting soil. To investigate the effect of foundation flexibility on the response of R/C free‐standing towers deforming into their inelastic range during intense ground shaking, a linear sway‐rocking model is applied in numerical modelling of the soil–structure system. The effect of concrete cracking and reinforcement yielding on the elements used in the structure modelling is taken into account by introducing a nonlinear model for R/C frame elements using the moment–curvature (M–ϕ) relation. A method called pseudo‐dynamic analysis is presented to quantify the inelastic seismic response spectrum of a soil–R/C free‐standing system using response spectrum analysis method and push‐over analysis technique. The earthquake responses of cracked and uncracked systems for a practical TV tower and a practical range of soil shear wave velocity are calculated and compared with the objective of understanding how soil–structure interaction influences structural responses. Copyright © 2002 John Wiley & Sons, Ltd.

State-of-the-art of advanced inelastic analysis of steel and composite structures

This paper provides a state-of-the-art review on advanced analysis models for investigating the load-displacement and ultimate load behaviour of steel and composite frames subjected to static gravity and lateral loads. Various inelastic analysis models for steel and composite members are reviewed. Composite beams under positive and negative moments are analysed using a moment-curvature relationship which captures the effects of concrete cracking and steel yielding along the members length. Beam-to-column connections are modeled using rotational spring. Building core walls are modeled using thin-walled element. Finally, the nonlinear behaviour of a complete multi-storey building frame consisting of a centre core-wall and the perimeter frames for lateral-load resistance is investigated. The performance of the total building system is evaluated in term of its serviceability and ultimate limit states.

Rotating crack finite element model for reinforced concrete structures

Presented in this paper is a rotating crack finite element model for the analysis of reinforced and prestressed concrete structures, loaded in the plane of the structure. The effects of concrete cracking and crushing, crack rotation, tension stiffening and bond-slip are considered. Discrete elements are used to model the concrete and steel with bond-slip incorporated into the formulation of the bar element used to model the steel reinforcement. Structures subject to either monotonic or cyclic loading may be analysed. The model has been incorporated into a finite element program for the analysis of reinforced concrete structures (program RECAP) and has been extensively tested against laboratory experiments with a high degree of corroboration. Two examples are presented to demonstrate that results obtained using the finite element model compare favourably with experimental data.

Modeling Damage to Rigid Pavements Caused by Subgrade Pumping

The efficient utilization of construction and maintenance resources requires the ability to effectively predict and model subgrade pumping in rigid concrete pavements. A review of the evolution of a rigid pavement pumping model is presented in this paper. Extensions were made to an existing model to consider the effects of climate and drainage conditions, as well as soil composition on pumping magnitudes. Additional modifications permit the effect of nonconventional vehicle configurations to be considered in the calculation of pumping values. Finally, the process of calculating pumping volumes and distributing void areas was altered to provide a more realistic effect. This improved model allows proposed designs to be analyzed to determine optimum pavement characteristics. The model is implemented in a finite-element-based method for analysis of pavements that also includes the effects of concrete cracking and fatigue. Urgent need for experimental data on the size and growth of voids beneath a pavement slab is pointed out.

Finite element modeling of reinforced concrete structures

This paper presents a reinforced concrete model for nonlinear finite element analysis. The model performs the nonlinear behaviors of both concrete and reinforcement steel in each element. The effects of concrete cracking, tension stiffening and dowel action are also considered in the new model. Numerical results, in comparison with experimental data, are presented.

Partial interaction analysis of double skin composite beams

Double skin composite beams are formed using steel plates connected to a concrete infill by means of welded stud shear connectors. This construction acts in a similar way to doubly reinforced concrete elements but the flexibility of connection between the steel plates and concrete gives rise to interface slip and additional overall element deflection. This paper presents a closed form solution for the analysis of simply-supported double skin composite beams. This method takes into account the flexibility of connection on both tension and compression faces and is extended to cover the effects of concrete cracking and non-linear connector behaviour using a step-wise linearisation technique. The analysis is compared against model and full scale experimental work that has been previously reported by the authors. It is concluded that the proposed method shows good correlation with real behaviour and may be reliably used for the analysis of simply supported double skin composite beams.

The cylinder splitting test as a method for determining the compressive strength of concrete

Research into the effects of concrete cracking caused, for instance, by alkali—silica reaction, has shown that the cylinder splitting or Brazilian test does not reflect the tensile strength but rather the compressive strength as would be measured from prisms with a height/width ratio of about 3. This Paper demonstrates that the cylinder splitting test may be used as a compression test using the appropriate bearing width, which is derived to be about one-seventh of the cylinder's diameter. If the bearing width is increased above one-third of the cylinder's diameter with special loading platens, the effective height/width ratio is reduced resulting in the same enhancement of measured compressive strength as occurs in the standard cube test. Practical use of the method in relation to alkali—silica reaction is described and the consequences are stated.

Effects of concrete cracking on the earthquake response of gravity dams

AbstractTensile stresses exceeding the tensile strength of concrete can develop in concrete dams subjected to earthquake ground motion. This study examines the earthquake response of gravity dams including tensile cracking of the concrete. The interaction between the dam and compressible water is included in the analysis using a numerical procedure for computing the non‐linear dynamic response of fluid‐structure systems. The crack band theory is used to model tensile cracking with modifications to allow for the large finite elements necessary for dam analysis. The earthquake response of a typical gravity dam monolith shows that concrete cracking is an important non‐linear phenomenon. Cracking is concentrated near the base of the dam and near the discontinuities in the face slope. The extensive cracking, which develops due to ground motion typical of maximum credible earthquakes, may affect the stability of dams during and after strong earthquakes.

Multidirectional Membrane Reinforcement

A method for analyzing local strength of reinforced concrete membranes reinforced with a multidirectional mesh and subjected to known in-plane internal forces is presented. Such structures occur often in practice, and include shear walls, floor diaphragms, folded plates, and shells. The effect of concrete cracking on the response of the shell under proportionately increasing loads is examined. The governing system of equations is derived, and a numerical, iterative procedure is developed to calculate local response at any load stage through ultimate. Gupta's conclusion that up to first yield crack direction remains constant and then rotates is confirmed. It is shown that at yield all bars are in tension, an ultimate ductile strength can be calculated from a simple relation; to obtain a time-history response, the method presented here has to be used. The procedure is illustrated with two numerical examples.

Seismic Analysis of Slender Coupled Walls

The dynamic response of multistory reinforced concrete coupled walls was evaluated from the perspective of linear models based on response spectra, modal analysis, and reduced effective stiffnesses. This study indicates that: (1) Linear models based on plausible reductions in stiffness and reasonable ductility demands in the structural components can provide an adequate basis for designing reinforced concrete structures; (2) the design of multistory reinforced concrete coupled walls must include the effects of concrete cracking, slip of the reinforcement, and ductility demands in the structural components. Special attention must be given to the redistribution of flexural moments and shear forces between the wall in tension and the wall in compression; (3) natural frequencies of reinforced concrete structures can be significantly reduced by cracking caused by shrinking of the concrete; and (4) to avoid catastrophic collapse in coupled wall systems, the structural system should be designed such that the coupling beams are the only members that suffer severe yield cycles, and their energy dissipation capacity is utilized before the walls are subjected to high or extreme ductility demands.