Curvature Ductility Capacity Research Articles

CURVATURE DUCTILITYOF REINFORCED CONCRETE BEAM SECTIONS STIFFENED WITH STEEL PLATES

This paper presents theoretical parametric study of the curvature ductility capacity for reinforced concrete beam sections stiffened with steel plates. The study considers the behavior of concrete and reinforcing steel under different strain rates. A computer program has been written to compute the curvature ductility taking into account the spalling in concrete cover. Strain rate sensitive constitutive models of steel and concrete were used for predicting the moment-curvature relationship of reinforced concrete beams at different rate of straining. The study parameters are the yield strength of main reinforcement, yield strength of transverse reinforcement, compressive strength of concrete, spacing of stirrups and steel plate thickness. The results indicated that higher strain rates improve both the curvature ductility and the moment capacity of reinforced concrete beam sections. Moreover the section curvature ductility increases as the thickness of the stiffening plates decreases.

Displacement Ductility Limits for Pile Foundations in Cohesionless Soils

ABSTRACTThe displacement ductility limit for seismic design of concrete piles is determined for the range of cohesionless soils expected in practice. The curvature ductility capacity associated with specified performance limit states, namely, the “serviceability” and “damage-control” limits, is determined based on the current provisions for confining steel. An analytical model is applied to assess the displacement ductility factor at the specified curvature ductility level. The investigated parameters include the soil stiffness, pile diameter, longitudinal reinforcement ratio, axial force level, and pile above-ground height. A set of design displacement ductility factors is recommended and verified to ensure the satisfactory seismic performance.

Displacement Ductility Capacity Assessment for a Fixed-Head Pile in Cohesionless Soil

AbstractThis study develops assessment formulas for the displacement ductility capacity of a fixed-head pile in cohesionless soils. The derivations of the formulas are based on an ideal model of a semiinfinite nonlinear pile in a Gibson soil, whose subgrade reaction modulus increases linearly with depth, to link the displacement ductility capacity of the pile with the pile–soil system parameters. The parameters in the formulas include the sectional overstrength ratio and curvature ductility capacity, as well as a modification factor for considering soil nonlinearity. The modification factor is a function of the displacement ratio of the pile’s ultimate displacement to the effective soil yield displacement, which is constructed through a number of numerical pushover analyses. The format of the formulas is similar to that for a pile in cohesive soils. For the case of linear soil, the formulas provide a lower-bound estimate of pile ductility capacity; the displacement ductility capacity of a pile in cohesion...

Seismic Performance Quantification of Reinforced Masonry Structural Walls with Boundary Elements

The design of reinforced masonry (RM) structural walls subject to high inelastic curvature demands can often be hindered by prescriptive requirements in design codes regarding the ratio between compression zone depth (c) and wall length (ℓw). A possible solution to this would be the detailing of a confined boundary element at the critical wall toes to increase the curvature ductility capacity of the plastic hinge region. The Masonry Standards Joint Committee (MSJC) code currently prescribes the possible use of such boundary elements for the special reinforced masonry shear walls category. However, the MSJC provides no relevant prescriptive detailing guidance, leaving the onus on the designer to specify appropriate detailing to ensure the desired performance. The results of an experimental program designed to develop a confinement scheme based on conventional masonry construction practices are reported in this paper. Five half-scale RM walls, detailed with confined boundary elements containing a double layer of vertical reinforcement enclosed by stirrups, were tested under reversed cycles of quasi-static loading. The walls, detailed to represent typical low- to medium-rise construction, varied by their height, length, and aspect and vertical reinforcement ratios. Test results are reported in terms of force-based seismic design parameters, such as the wall strength, stiffness and ductility characteristics, as well as displacement and performance-based seismic design parameters for the next-generation of seismic codes in North America. Overall, the performance of the walls indicates that the selected boundary element detailing is a designer-friendly means of addressing the need for lower c/ℓw ratios and higher curvature levels as indicated by the MSJC.

Simplified Procedure for Seismic Evaluation of Piles with Partial-Moment Connection to the Deck in Marine Oil Terminals

This paper presents development of a simplified procedure for seismic evaluation of piles with partial-moment connection typically used in marine oil terminals. The current seismic evaluation procedure of the piles in marine oil terminals includes monitoring material strains specified in the Marine Oil Terminal Engineering and Maintenance Standard (MOTEMS) during the nonlinear static pushover analysis to estimate the displacement capacity of piles. This investigation developed closed-form formulas for estimating the displacement capacity of piles by using a simple pile-deck connection system. The displacement capacity estimated from these formulas ensures that the material stain limits specified in the MOTEMS is not exceeded. These formulas are demonstrated to be accurate by comparing results from these formulas against those from the nonlinear finite-element analysis. The formulas developed in this investigation utilize the curvature ductility capacity of the pile section and rotation ductility capacity of the connection at the selected seismic design level, along with the parameter β which depends on the relative stiffness of the pile and the connection and the parameter η which depends on the relative strength of the connection and the pile.

Proportioning of steel beam–column members based on RSD optimization methodology

Due to the cost and energy embodied in steel production, a reduction in the cross-sectional area of a steel structural member could imply a significant saving of money and reduction in greenhouse gas emissions. Hernandez-Montes et al. [Hernández-Montes E, Aschheim M, Gil-Martin LM. The impact of optimal longitudinal reinforcement on the curvature ductility capacity of reinforced concrete column sections. Mag Concrete Res 2004;56(9):499–512; Hernández-Montes E, Gil-Martín LM, Aschheim M. The design of concrete members subjected to uniaxial bending and compression using reinforcement sizing diagrams. ACI Struct J 2005;102(1):150–8] proposed an analytical approach for reducing the amount of longitudinal reinforcement in reinforced concrete members subjected to the action of axial force and bending moment acting about a principal axis of the cross-section. The approach, which makes use of Reinforcement Sizing Diagrams (RSD), makes use of a graphical representation of all possible reinforcement solutions for a particular concrete cross-section subjected to a combined loading consisting of bending moment and axial load ( M , N ) . The common symmetric solution is recognized as just one of the infinite number of possible solutions. The RSD methodology used in that approach is extended in the present paper to steel sections having at least one axis of symmetry, subjected to axial force, bending moment about the strong axis, and shear acting in the plane of the bending moment. Special considerations are introduced to address the instabilities associated with slender steel elements. The methodology is developed following the Eurocode 3 provisions for compact steel members.

Evaluation of Moment Distribution in Continuous Fiber-Reinforced Polymer-Strengthened Concrete Beams

Fiber-reinforced polymer (FRP) strengthening offers many well-documented benefits for the retrofit of existing reinforced concrete (RC) structures. The main drawback in using FRP for such applications, however, is the reduction in ductility capacity after strengthening. This loss in ductility has led worldwide codes to not consider redistribution of bending moments in continuous FRP-strengthened RC beams. This implies that an unstrengthened continuous RC beam that was previously designed under assumptions of moment redistribution (MR) and is to be strengthened with FRP must now be redesigned according to full elastic distribution of bending moments. This could lead to onerous conditions in such strengthening applications. This paper sets out a rationale for the possible appropriate use of redistribution principles for FRP-strengthened beams. Analytical results show that if a section can develop a curvature ductility capacity greater than 2.0, it is likely that redistribution in the order of at least 7.5% can be achieved. These results are presented and further discussed in this paper. © 2008, American Concrete Institute.

CURVATURE DUCTILITYOF REINFORCED CONCRETE BEAM SECTIONS STIFFENED WITH STEEL PLATES

This paper presents theoretical parametric study of the curvature ductility capacity forreinforced concrete beam sections stiffened with steel plates. The study considers the behavior ofconcrete and reinforcing steel under different strain rates. A computer program has been written tocompute the curvature ductility taking into account the spalling in concrete cover. Strain ratesensitive constitutive models of steel and concrete were used for predicting the moment-curvaturerelationship of reinforced concrete beams at different rate of straining. The study parameters are theyield strength of main reinforcement, yield strength of transverse reinforcement, compressivestrength of concrete, spacing of stirrups and steel plate thickness. The results indicated that higherstrain rates improve both the curvature ductility and the moment capacity of reinforced concretebeam sections. Moreover the section curvature ductility increases as the thickness of the stiffeningplates decreases.

Curvature Ductility of Reinforced Concrete Column Sections Under Different strain Rates

This paper presents theoretical parametric study of the curvature ductility capacity for reinforced concrete column sections. The study considers the behavior of concrete and reinforcing steel under different strain rates. A computer program has been written to compute the curvature ductility taking into account the spalling in concrete cover. Strain rate sensitive constitutive models of steel and concrete were used for predicting the moment-curvature relationship of reinforced concrete columns at different rate of straining. The study parameters are the yield strength of main reinforcement, yield strength of transverse reinforcement, compressive strength of concrete, spacing of ties and the axial load. The results indicated that higher strain rates improve both the curvature ductility and the moment capacity of reinforced concrete column sections.

Impact of optimal longitudinal reinforcement on the curvature ductility capacity of reinforced concrete column sections

The traditional practice of providing symmetric reinforcement in column cross-sections has been shown to be non-optimal for columns subjected to non-symmetric design loads. An approach for determining a continuum of acceptable combinations of reinforcement by means of a reinforcement sizing diagram (RSD) has been described recently. This approach allows the minimum (or optimal) reinforcement of a cross-section to be determined based on strength considerations. This paper compares the curvature ductility capacity of cross-sections designed with optimal reinforcement to that obtained for cross-sections having symmetric reinforcement, for discrete values of axial load between 0% and 65% of Agfck, where Ag is the gross section area and fck is the concrete compressive strength. Unconfined concrete and confined concrete behaviour are considered, with the latter based on the Mander model, for confinement satisfying the requirements of ACI-318-02 for high seismic zones. The use of non-symmetric longitudinal reinforcement is determined to cause small to moderate changes in the computed curvature ductility capacities relative to the values computed for conventionally reinforced columns.

Impact of optimal longitudinal reinforcement on the curvature ductility capacity of reinforced concrete column sections

Impact of optimal longitudinal reinforcement on the curvature ductility capacity of reinforced concrete column sections

Assessment of seismic performance of extended pile‐shafts

AbstractThe seismic performance of extended pile‐shafts subjected to the current level of displacement ductility demand is assessed for different soil conditions. Local curvature ductility demand is compared with the curvature ductility capacity provided by the current level of confining steel. Parameters in the assessment of extended pile‐shafts include the undrained shear strength of cohesive soils, relative density of cohesionless soils, aboveground height, longitudinal reinforcement ratio, axial force level and pile diameter. Results indicate that the curvature ductility demand in the pile decreases with increased soil stiffness but increases with increased aboveground height. The curvature ductility demand however is not sensitive to the longitudinal reinforcement ratio or axial force level, and is independent of the pile diameter. Results further indicate that the curvature ductility capacity available from the current level of confining steel may not be adequate for tall extended pile‐shafts, especially for piles with large longitudinal reinforcement ratio and embedded in soft or loose soils. Limits on the maximum longitudinal reinforcement ratio are suggested in the paper. Copyright © 2003 John Wiley & Sons, Ltd.

AN ANALYSIS OF THE SEISMIC CHARACTERISTICS OF STEEL-JACKETED CIRCULAR BRIDGE COLUMNS

The current approach for seismic retrofit of deficient bridge columns in California involves extensive use of steel jacketing. In this paper, the influence of steel jacketing on the lateral response of circular bridge columns is studied; particularly, the enhancement of the ultimate compressive strain of concrete, the increase in curvature ductility capacity and the increase in lateral stiffness are investigated. The current steel jacket thickness used in California is shown to enhance the ultimate compressive strain of concrete by 4-9 times the spalling strain of unconfined concrete. For larger steel jacket thickness, the ultimate limit state of steel-jacketed columns may be governed by the low-cycle fatigue fracture of the longitudinal reinforcement instead of the ultimate compressive strain of concrete. Steel jacketing is also expected to increase significantly the lateral stiffness of columns if full-height steel jackets are used. The increase in lateral stiffness of flexural columns (3 ≤ L/D ≤ 9) is estimated to be 35-60 per cent using current jacket thickness. Inelastic dynamic analyses of steel-jacketed columns using ground motions recorded during the 1989 Loma Prieta earthquake indicated that the current steel jacket thickness provides adequate protection against the damage potential of the ground motions with comparable spectral acceleration as that specified in current design spectra, and the damage sustained by the steel-jacketed column is likely to be repairable.