Capacity Design Approach Research Articles

The Seismic Performance Evaluation of An Eccentrically Braced Steel Frame by Non-Linear Analyses

The goal of this paper is to investigate the non-linear response and to assess the seismic performance of a six story eccentrically braced steel frame (EBF). For this, split-K-braced EBF with high ductility level designed according to the Turkish Earthquake Code-2007 (TEC-07) is analyzed under seven selected earthquake records. The performance of the EBF is assessed considering drift, story and base shear demands, brace and column axial forces and bending moment demands, link beam shear force and rotation demands. Mean values of the demands are used in the performance assessment. The provisions based on capacity design approach specified in TEC-07 for EBFs with high ductility level are discussed by employing the findings.

Capacity Design of Retaining Structures and Bridge Abutments with Deep Foundations

This paper examines a seismic capacity design approach for retaining structures with piled foundations, which assumes full-strength mobilization in the soil and in the foundation piles during the earthquake. The plastic mechanism activated by the seismic forces consists of a horizontal movement of the structure, involving plastic hinging in the piles. This mechanism is triggered when the seismic inertial forces acting within the structure and the soil mass equal the overall strength of the soil-pile foundation system. The paper describes an iterative procedure for evaluating the critical seismic acceleration that activates the plastic mechanism. The seismic performance of the structure is expressed by its permanent displacements and the corresponding curvature ductility demand in the foundation piles. With reference to an idealized bridge abutment, this procedure is expressed in a fully consistent nondimensional form and is applied to a reference case, to show its potentiality and to discuss the influence of a number of key parameters, such as the soil strength and the foundation geometry on the seismic performance of the structure.

Shear strength of panel zone in beam-to-column connections

The paper deals with the problem of evaluation of the panel zone (PZ) shear strength in beam-to-column connection. To this aim, the mechanical behaviour of the PZ and the European and American code provisions for the design of PZ are examined and critically discussed. Non-linear FEM analyses and experimental tests carried out on beam-to-column steel connections are also provided and compared with both European and American practices. Both numerical and experimental results have shown a good agreement with the American provisions. On the contrary, some drawbacks are identified in the application of European provisions, which cause overestimation of the PZ shear strength of about 50–60%. These differences could cause invalidation of the capacity design approach to the steel moment resisting frames, which in the case of European provisions should lead to strong panel zone, where the possibility of PZ yielding is precluded. Therefore, an improvement to the European code provisions is suggested in order to better evaluate the PZ shear strength.

Ductile moment-resistant steel–timber connections

This paper investigates the mechanical characterisation of a joint, suitable for different configurations within a heavy timber frame, consisting of a wooden element connected to a steel stub by means of an end-plate and glued-in steel rods. This connection system has some interesting properties in terms of mechanical performance, versatility and prefabrication. An analytical model to predict the joint response in terms of its key parameters (e.g. failure mode, ultimate resistance, stiffness and rotation capacity) is proposed and validated through an extensive experimental programme. The component method, originally proposed for semi-rigid joints in steel frameworks, is adapted in order to set up a feasible general model for steel–timber joints, enabling application of the capacity design approach and offering the required ductility for applications in seismic zones. The tests carried out indicate satisfactory agreement between theoretical and experimental results: the reliable prediction of joint failure modes allows design of moment-resistant connections that can sustain high plastic deformation without brittle rupture, with a remarkable degree of global ductility and energy dissipation under alternate loading.

Application of Indirect Capacity Design Principles for Seismic Design of Steel-Plate Shear Walls

This paper presents a capacity design procedure that aims to achieve good seismic performance for steel-plate shear walls and improve the overall economy of the system. The proposed method uses indirect capacity design principles to identify the infill plates most likely to yield in the design earthquake. Linear models of the boundary columns are used to determine the column design forces. The proposed method is used for the design of two 4-story and one 8-story steel-plate shear walls. Design axial forces and moments in the boundary columns for the three different steel-plate shear walls are compared with nonlinear seismic analysis results, and the results of the proposed procedure are shown to be in good agreement with those of the nonlinear analyses. For comparison, the paper also evaluates other capacity design approaches that have been proposed in the literature.

A Comparative Study on Structural Wall Design Approach of 2007 Turkish Earthquake Code

The current version of the Turkish Earthquake Code (TEC-07) was released in 2007 and the capacity design approach for high ductility structural walls was introduced for the first time. The practicing engineers, however, mentioned various problems especially related with the shear design section of high ductility structural walls. Because of this reason, an in-depth comparative study was conducted to examine the differences and similarities of the design approaches of TEC-07, American Reinforced Concrete Code (ACI 318-08) and various studies in the literature that focus on capacity design of structural walls. In addition to this, differences between normal ductility structural walls of TEC-07 and ordinary walls of ACI 318-08 were also examined. It was observed that in the current version of the TEC-07, several clauses related to structural wall design needs further considerations. Several modifications were proposed in order to improve the structural wall design of the current code.

A Discussion on some Key Issues for Seismic Design of Concentrically Braced Frames According to Canadian and Chinese Codes

To gain further insight into the seismic design of concentrically braced frames as defined by the Canadian and Chinese codes, a comparison of the main design requirements contained in each code is carried out in this paper. The comparison emphasizes on the differences existing in these two code provisions, and the reasons behind them. The issues that are examined include the seismic force resisting systems for braced frames, the height restrictions, the force transferred to the beams in chevron configurations, the slenderness ratios of the bracing members, the width-to-thickness ratios of the brace sections, and the influence of brace connections on the columns. Some additional issues that still remain undefined on the seismic response of these systems and some proposals for further studies are also discussed. It is concluded through this comparison that a number of modifications are still required in order to fully implement a capacity design approach of these systems in both codes.

Plastic Design of Seismic Resistant V-Braced Frames

In this article, a new method for designing chevron concentrically braced steel frames is presented. The aim of the proposed method is the design of concentrically braced steel frames able to guarantee, under seismic horizontal forces, a collapse mechanism of global type. This result is of great importance in the seismic design of structures, because local failure modes give rise to a worsening of the energy dissipation capacity of structures and, therefore, to an higher probability of failure during severe earthquakes. With reference to the examined structural typology, the global mechanism is characterized by the yielding of tensile bracing diagonals and by the buckling of the compressed diagonals of all the stories. The proposed method is rigorously based on “capacity design approach” which requires that dissipative zones have to be designed to withstand the internal actions due to the seismic design horizontal forces and the vertical loads acting in the seismic load combination; while non dissipative zones have to be designed considering the maximum internal actions that dissipative zones, yielded and strain-hardened, are able to transmit. The new design issue covered by the proposed design procedure is the need to account for the contribution of the compressed diagonals in deriving the design axial force of non dissipative members. The seismic inelastic response of a sample structure is investigated by means of nonlinear dynamic analyses. The results carried out with reference to braced frames designed according to the proposed procedure are compared with those obtained with reference to the same structural schemes designed according to Eurocode 8.

Seismic analysis of steel plate shear walls considering strain rate and [formula omitted]–delta effects

Nonlinear seismic responses of a typical 15-storey and 4-storey steel plate shear wall are studied. Dynamic shear and moment envelopes are compared with the current CAN/CSA-S16-01 seismic capacity design approach. It has been observed that estimated dynamic base shear forces and overturning moments in the steel plate shear walls, as well as the column forces, are underestimated in the current seismic design provisions. The effect of loading rate on the dynamic behaviour of steel plate shear walls is also investigated. Nonlinear dynamic analyses show that loading rate increases flexural demand mostly at the base of the steel plate shear wall and loading rate has a small effect on inelastic seismic demand for a suite of spectrum compatible earthquake records for Vancouver. Also investigated is the P –delta effect on seismic demand in shear and flexure. The inelastic seismic analyses indicate that the current National Building Code of Canada stability factor approach to account for P –delta effects is very conservative for steel plate shear walls and the P –delta effects on seismic demand are very small.

LIMIT PERIOD BASED ON APPROXIMATE ANALYTICAL METHODS ESTIMATING INELASTIC DISPLACEMENT DEMANDS OF BUILDINGS

The Algerian seismic design code (RPA99) recommends a limit on the elastic period as a governing factor in the design process of low and mid‐rise buildings, function of the structural system regardless of the related ductility level. The recommended limit criterion is evaluated through approximate analytical methods using drift limit. The assignable displacement ductility ratio for the force reduction factor is derived from some well established R‐μ‐Tn expressions. The limit period evaluation procedure (proposed in this paper) agrees with a capacity design approach since it allows for adjusting the required resistance demand level function of a ductility level resulting from code's steel recommendations. This will enhance seismic design procedure based on a target‐period approach such as in the Algerian seismic design code RPA99, to fulfil the minimum required two performance levels or to satisfy three performance levels if a damage control is considered. A critical study is carried out considering three regular earthquake‐resistant concrete framed structures and taking into account the specificity of various types of soils, namely rock, firm and soft. A comparison of the obtained results shows clearly that the RPA99 recommended limit is only valid for nude moment resisting frames.

Reply to the discussion by Richard Redwood and Patrick Paultre on "Making use of brace overstrength to improve the seismic response of multistorey split-X concentrically braced steel frames"

The authors agree that P-delta effects are typically more significant for structures designed for lower seismic loads. The authors also agree that, as indicated in the conclusion of the paper, the proposed enhanced storey ductility redistribution capacity (ESDRC) design approach resulted in improved seismic response when used in combination with design seismic loads amplified for P-delta effects.

Some controversial aspects of the seismic design of reinforced concrete building structures

Significant differences exist between the recommendations for seismic design of the codes and guidelines for reinforced concrete of different countries. Performance criteria for building structure to avoid unacceptable damage during various levels of earthquake hazard need to be refined. More accurate recommendation for the effective flexural rigidity of reinforced concrete members are required for linear elastic structural analysis to enable better estimates of the periods of vibration and the lateral deflections of statically indeterminate structures including the effects of cracking of concrete. Current code recommended values for flexural rigidity will generally lead to estimates of the periods of vibration and lateral deflections, which are on the low side. The capacity design approach to ensure the most appropriate mechanism of yielding will occur in the event of a severe earthquake is generally recognized by codes but to varying degrees of clarity, and the degrees to which capacity design is incorporated in each code varies significantly. High strength concrete and high strength non-prestressed steel reinforcement can be used in the design of buildings but the brittle behaviour of high strength concrete and the unusable yield strength of high strength steel reinforcement need to be considered. Important differences between codes exist in the rules for the quantity of confining reinforcement placed in reinforced concrete columns to ensure ductile behaviour. Significant differences also exist between the quantities of shear and confining reinforcement required in beam-column joints and in the anchorage of length of longitudinal reinforcement passing through beam-column joints. Precast concrete structures can be designed successfully for earthquake resistance but design codes in seismic regions contain provisions for precast concrete to varying degrees.

Developments in seismic design procedures for bridges in New Zealand

Progress on developments in the seismic design procedures for bridges in New Zealand is outlined. The current approach has evolved from the recommendations of a study group of the New Zealand National Society for Earthquake Engineering which was published in 1980. Research and development into the determination of the design seismic force and ductility demand, the capacity design approach, the detailing of bridge columns for adequate ductility, and the design approach using seismic isolation are discussed. More recent developments in New Zealand involving the assessment and retrofit of older bridge structures are also discussed and likely activities and needs of the next decade are suggested.

Concrete Capacity Design (CCD) Approach for Fastening to Concrete

A user-friendly, highly transparent model for the design of post-installed steel anchors or cast-in-place headed studs or bolts, termed the concrete capacity design (CCD) approach, is presented. This approach is compared to the well-known provisions of the American Concrete Institute (ACI) 349-85. The use of both methods to predict the concrete failure load of fastenings in uncracked concrete under monotonic loading for important applications is compared. Variables included single anchors away from and close to the edge, anchor groups, tension loading, and shear loading. A data bank including approximately 1,200 European and American tests was evaluated. The comparison shows that the CCD method can accurately predict the concrete failure load of fastenings for the full range of investigated applications. On the other hand, depending on the application in question, the predictions of ACI 349 are sometimes unconservative and sometimes conservative. The CCD method is more user-friendly for design. Based on this, the CCD method is recommended as the basis for the design of fastenings.

Column strength requirements in multi-storey seismic frames

This paper examines factors affecting the strength requirements of columns in multi-storey frames responding to seismic ground motions. The examination is carried out using an inelastic static analysis approach and the concept of an "equivalent condensed frame". In particular, the influence of higher modes and the effect of varying the pattern of beam flexural strength over the frame height are evaluated. It is suggested that the current capacity design approach of the NZ Concrete Design Code overstates the importance of higher mode effects while neglecting the potentially more important influence of the beam flexural strength pattern that is provided for a frame. Some tentative modifications to the current column design procedure are suggested for future evaluation under inelastic dynamic response conditions.

The performance of a ductile moment resisting connection between a precast concrete column and a timber beam

A ductile moment resisting joint suitable for the connection of a precast concrete column to a glued laminated timber beam is described. The design, fabrication and test performance of four variants of the joint which was fabricated from structural steel components are described in detail. The design was strongly constrained by practical considerations including the requirement that it be capable of attachment to both the beam and column at the time of erection, that wide construction tolerances be accommodated at the erection stage and that its fabrication could readily be undertaken by precast concrete and structural steel fabricators without special facilities. A capacity design approach for the joint was followed, based on the current New Zealand structural steel and structural concrete codes of practice. The design of the test joints was based on a defined strength hierarchy intended to result in large inelastic deformations being localised to the structural steelwork components. These components performed well in the tests. Some of the precast column sections tested were insufficiently reinforced for shear. Although confinement reinforcement was not provided for the purpose and it was not intended that they themselves be ductile, those precast concrete column sections with adequate shear reinforcement appeared to be capable of sustaining moment through a limited number of inelastic reverse cycle rotations even without confinement reinforcement. It appears that if such a joint is to be developed further, the inelastic rotational capacity, of the concrete column itself may more reliably provide the required ductility if confinement reinforcement is provided at the hinge position.

A procedure for the analysis and design of ductile reinforced concrete frame buildings of moderate height

A procedure is presented in step by step form for designing and detailing a reinforced concrete frame building to the requirements of DZ4203 (Draft New Zealand loading code). Consideration is given for adequate ductility by means of a capacity design approach to all members to obtain a large number of plastic hinges which are detailed to dissipate energy without brittle failure. Further ductile detailing is given for all other locations where accidental hinges could occur and to limit excessive deflections that may result from deterioration of beam column joints.