Seismic Resistant Steel Frames Research Articles

Theory of plastic mechanism control: A new approach for the optimization of seismic resistant steel frames

AbstractThis paper presents an important improvement in seismic design of structures based on the application of the Theory of Plastic Mechanism Control (TPMC). TPMC was originally proposed in the ‘90s requiring an iterative algorithm and upgraded in 2015 leading to the so‐called closed form solution. In the recent years, TPMC has shown its value as an effective design procedure which can be applied to any structural typology. Moreover, it has been used as a code competitor design tool in important RFCS founded research projects confirming its effectiveness, simplicity, and suitability to any structural typology. The aim of the TPMC is the design of structures able to exhibit at collapse a global type mechanism. The TPMC was originally based on the extension of the kinematic theorem of plastic collapse to the concept of mechanism equilibrium curve, working in the plane (being α the multiplier of the seismic forces and δ the top sway displacement). The novelty of this work is improvement of the design procedure by working in the plane, being θ the plastic rotation. This new TPMC approach, namely TPMC(θ), has demonstrated to be as reliable as the former approach, thus leading to structures able to develop a collapse mechanism of global type but with the optimization of the structure using lighter columns. The effectiveness of the new procedure has been confirmed by both pushover and dynamic non‐linear analyses.

The design of steel constructions in seismic conditions

In this article, the principles of designing of seismic resistant steel frames of industrial buildings are considered. The particular attention is paid to the damage causes of the steel frames under the seismic loads affects, and to the requirements that must be considered while designing the steel frames in seismically active areas. The most suitable materials that can be used to strengthen the steel frames have been studied. The strengthening is possible due to the frame’s proper operating in accordance with arising seismic loads. The analysis of the loads, which are calculated according to the regulatory documents of Russia and other countries, is presented. As well, the loads have been compared to each other. There is a review of possible experimental methods to determine the frame’s strength under the seismic loads in the article. In addition, there are some critics on the existing regulatory documents and on, exactly, the formulas and coefficients used, as well as on the proposed alternative solutions. We have made the research of the effect that soil has on the steel frame’s strength characteristics under the seismic loads. Promising constructive solutions for steel frames in case of earthquakes are indicated. The experience of designing the earthquake-resistant structures in other countries has been studied. The materials and documents about the past accidents in Russia and world’s other countries have been analyzed. The studying of the influence of the steel frames own vibrations and their constructional forms on the foundation’s pliability is also presented here.

Self-centering steel column base with metallic energy dissipation devices

Column bases of seismic-resistant steel frames are typically designed as full-strength to ensure that plastic hinges develop in the bottom end of the first-storey columns. Alternatively, column bases may be designed as partial-strength and dissipate energy through inelastic deformations in their main components (i.e., base plate, steel anchor rods). Both design philosophies result in difficult-to-repair damage and residual drifts. Moreover, the second design philosophy results in complex hysteretic behaviour with strength and stiffness deterioration. This paper proposes a partial-strength low-damage self-centering steel column base. The column base provides flexibility in the design as its rotational stiffness and moment resistance can be independently tuned. The paper presents an analytical model that predicts the stiffness, strength, and hysteretic behaviour of the column base. In addition, a design procedure and detailed finite element models are presented. The paper evaluates the effectiveness of the column base by carrying out nonlinear dynamic analyses on a prototype steel building designed as post-tensioned self-centering moment-resisting frame. The results demonstrate the potential of the column base to reduce the residual first-storey drifts and protect the first-storey columns from yielding.

Full strength extended stiffened end-plate joints: AISC vs recent European design criteria

Extended stiffened end-plate bolted joints are widely used in seismic resistant steel frames. In the United States of America (USA) this type of joint is seismically pre-qualified according to AISC 358-16. At the present time, prequalification criteria for different types of bolted joints are also under development in Europe within the framework of the EQUALJOINTS (i.e. European pre-QUALified steel JOINTS) research project. The design criteria and detailing rules proposed by this European project for extended stiffened end-plate joints differ from AISC criteria in some respects. Therefore, the aim of this work is to verify and to compare the effectiveness of both design procedures through the results of a comprehensive parametric study based on finite element (FE) simulations. The FE results show that both AISC and European design procedures can guarantee the formation of a plastic hinge in the beam under cyclic loading. However, under column loss scenarios the European connections are more ductile than those designed according to both AISC 358-16 and AISC 341-16. In addition, it is investigated the possibility to use heavy columns satisfying the resistance requirements without stiffeners (i.e. continuity plates and supplementary web plates). The comparison between the response of the joints with and without stiffened columns shows that heavy unstiffened columns can be adopted without appreciably modifying the joint response.

03.19: Seismic performance of full strength extended stiffened joint: American vs New European approach

ABSTRACTExtended stiffened end‐plate bolted joints are widely used in seismic resistant steel frames. In the United States of America (USA) this type of joint is seismically pre‐qualified according to AISC 358. In Europe prequalification criteria are under development within the framework of the ongoing EQUALJOINT research project. Even though the design rules of both approaches are based on the principles of hierarchy of resistances, there are some differences. In order to clarify these aspects, this paper describes both design criteria and rules. In addition, the results of a large parametric finite element investigation are used for discussion.

Seismic design of extended stiffened end-plate joints in the framework of Eurocodes

Bolted extended stiffened end-plate beam-to-column joints are widely used in seismic resistant steel frames. The flexural behaviour of this type of joints is crucial in order to guarantee an adequate seismic response. Eurocode 3 part 1–8 provides design rules and analytical models to predict the mechanical behaviour of the joints. Eurocode 8 provides additional design rules for seismic resistant joints, contradicting some requirements of Eurocode 3. In addition, in Eurocode 3 the influence of the rib stiffeners on the flexural response of this type of joints is not clearly accounted for. In this paper the criticisms of current versions of Eurocode 3 and Eurocode 8 are discussed and design criteria for seismic resistant extended stiffened end-plate beam-to-column joints are proposed. In addition, the results obtained from parametric finite element simulations are presented in order to support the discussion and to validate the design procedure.

Design of X-shaped double split tee joints accounting for moment–shear interaction

Dealing with steel moment resisting frames (MRFs), the latest version of Eurocode 8 allows us to dissipate the seismic input energy in connections provided that their characteristics under cyclic loads are certified by means of experimental testing. Within the beam-to-column joint typologies to be used in seismic resistant steel frames, the double split tee joint (DST) represents an interesting solution due to its easy fabrication and repair after a destructive seismic event. Nevertheless, the cyclic behavior of this joint typology is usually characterized by pinching and strength degradation phenomena due to the plastic engagement of the rectangular T-stubs which compromises the use of DST joints as dissipative elements. Within this framework, in this paper, in order to improve the hysteretic behavior of this connection typology, a new type of dissipative DST joint is presented. In particular, the proposed dissipative T-stub is designed substituting the rectangular T-stubs with the so-called X-shaped T-stubs, whose flange plates are cut into an hourglass shape similar to that of ADAS dampers. In particular, in the paper, a model that is able to predict the resistance of the proposed X-shaped T-stubs accounting for moment–shear interaction is developed and rules for designing the optimum shape of dissipative DST joints are proposed. Finally, the results of an experimental activity on real scale joints are presented aiming to verify the reliability of the proposed design approach and to compare the cyclic behavior of classical and X-shaped DST joints evidencing the benefits provided by the proposed dissipative joint.

Seismic behavior of frames with innovative energy dissipation systems (FUSEIS 1-1)

After strong earthquakes conventional frames used worldwide in multi - story steel buildings (e.g. moment resisting frames) are not well positioned according to reparability. Two innovative systems for seismic resistant steel frames incorporated with dissipative fuses were developed within the European Research Program "FUSEIS" (Vayas et al. 2013). The first, FUSEIS1, resembles a vertical Vierendeel beam and is composed of two closely spaced strong columns rigidly connected to multiple beams. In the second system, FUSEIS2, a discontinuity is introduced in the composite beams of a moment resisting frame and the dissipative devices are steel plates connecting the two parts. The FUSEIS system is able to dissipate energy by means of inelastic deformations in the fuses and combines ductility and architectural transparency with stiffness. In case of strong earthquakes damage concentrates only in the fuses which behave as self-centering systems able to return the structure to its initial undeformed shape. Repair work after such an event is limited only to replacing the fuses. Experimental and numerical investigations were performed to study the response of the fuses system. Code relevant design rules for the seismic design of frames with dissipative FUSEIS and practical recommendations on the selection of the appropriate fuses as a function of the most important parameters and member verifications have been formulated and are included in a Design Guide. This article presents the design and performance of building frames with FUSEIS 1-1 based on models calibrated on the experimental results.

Innovative Systems for Seismic Protection of Precast Industrial Buildings

An innovative dissipative (INERD Pin) connection system, which was previously developed for seismic resistant X-braced steel frames, was applied to retrofit existing precast industrial buildings designed only for gravity loads. Nonlinear dynamic analyses were carried out and the effectiveness of the dissipative connection system was evaluated. The INERD Pin connection system increased both the deformation capacity and the stiffness of the buildings, reducing damage of the structural elements. In case of low seismic actions, the INERD Pin connection system especially enhanced the stiffness of the structure, causing only small reductions of column rotations and top displacements. In case of severe seismic actions, the addition of the dissipative connections showed all its effectiveness particularly for low rotation capacity at column base, increasing the energy dissipation capacity and reducing the displacements of the structure. The results of the numerical investigations demonstrated the possibility to reduce the seismic vulnerability of existing precast buildings by means of dissipative connection systems.

Innovative seismic‐resistant steel frames (FUSEIS 1‐2) – experimental analysis

AbstractTwo innovative systems of seismic‐resistant steel frames with dissipative fuses were developed within the European Research Programme “FUSEIS”. The first, named FUSEIS 1, resembles a shear wall, whereas in the second system, named FUSEIS 2, the devices are made by introducing a discontinuity into the composite beams of a moment‐resisting frame. The main advantage of “FUSEIS” compared with conventional systems is that inelastic deformations are strictly concentrated and controlled in zones that constitute easily replaceable fuses. The dissipative elements can be positioned in small areas of the building and do not interrupt the architectural plan as braces do. Another advantage of the system is the possibility of easy installation and removal within the structure.This article presents the results of the experimental and analytical investigations of the innovative energy dissipation system FUSEIS 1. The system consists of two closely spaced strong columns connected by dissipative beams within each storey. In order to enhance the stiffness, strength and energy dissipation capacity of the system, several fuses are provided within each storey. During a strong seismic event, the dissipative zones are formed within the pins while the other parts of the structure remain elastic and protected.

Experimental analysis of seismic resistant composite steel frames with dissipative devices

This article presents the results of the experimental research performed at Politecnico di Milano, within the project Fuseis. The research project aims at developing innovative types of seismic resistant composite steel frames with dissipative fuses. In case of strong seismic events, damage will concentrate only in these fuses, without observing any significant damage in the structural elements such as steel beams, columns and reinforced concrete slab of the structure. After the seismic event, the repair work will be limited only to replacing the fuses. Four full scale tests are implemented in order to evaluate the performance of a composite steel frame with fuse devices under seismic actions in terms of moment rotation behavior of the joints, global energy dissipation, storey drift and frame stability.

Development of a Cast Modular Connector for Seismic-Resistant Steel Moment Frames Part II: Experimental Verification

A companion paper (Development of a Cast Modular Connector for Seismic-Resistant Steel Frames, Part 1: Prototype Development) describes the development of a prototype design for a cast modular connector (MC) for seismic-resistant steel moment frames. The eventual design, termed the MC "Beta"ť prototype design, was developed through a comprehensive analytical program that focused on the monotonic response of isolated connectors. Analyses of the MC Beta prototype design indicate the potential for excellent ductility and energy dissipation characteristics. This paper focuses on the prototyping and experimental verification of the MC Beta prototype. Steel foundry industry partners cast the MC Beta prototype at approximately half-scale. The scaled MC Beta prototype was tested in isolated fashion under monotonic and cyclic loading. The experimental results confirmed the performance of the analytically-based designs. The MC Beta prototype exhibited exceptional performance in terms of stable energy dissipation, far exceeding qualifying rotational ductility capacities. In direct comparisons to a WT (structural tee) section of similar stiffness and strength, the MC Beta prototype possessed greatly enhanced ductility and energy dissipation characteristics. With the MC Beta prototype developed and experimentally verified under isolated conditions, future work involves comprehensive analytical evaluation and full-scale experimental verification of beam-to-column joints containing the MC using accepted testing protocols and developing a design procedure for moment frames using the MC.

SEISMIC DESIGN OF STEEL FRAMES WITH PARTIAL STRENGTH JOINTS

In the seismic design of steel frames, beam-to-column joints can be designed either as full strength joints, forcing the location of the plastic hinges at the beam ends, or as partial strength joints which have to dissipate the seismic input energy. Seismic codes provide specific design criteria for full strength joints, but there are no detailed recommendations dealing with partial strength connections. Therefore, in this paper, by means of a simplified model, such as a SDOF system, the requirements which partial strength joints have to possess, for designing steel frames characterised by seismic performances equivalent to those of steel frames with rigid full strength joints, are pointed out. Successively, starting from the above requirements, a new method for designing seismic resistant steel frames with extended end plate connections leading to the complete definition of the geometrical and mechanical parameters of the joints is proposed.

Experimental Investigation of Reduced Beam Section Moment Connections without Continuity Plates

The AISC 2002 Seismic Provisions for Structural Steel Buildings recommend that usage and sizing of beam flange continuity plates across the column web shall be based on tests. The Recommended Seismic Design Criteria for New Steel Moment-Frame Buildings ( FEMA-350) state that unless project-specific testing is performed to demonstrate that continuity plates are not required, moment-resisting connections should be provided with continuity plates when the thickness of the column flange is below a minimum value. One of the preferred moment connections for seismic-resistant steel frames is the reduced beam section (RBS) moment connection, which has performed well under cyclic loads in laboratory testing. To demonstrate the effectiveness of the RBS moment connection without continuity plates in the panel zone, a series of four full-scale tests of exterior beam-column connections was carried out. All materials were A572 Grade 50 steel; the beams were W30×132, two of the assemblies used W14×283 columns, and the other two used W18×211 columns. The beams were welded to the columns using complete joint-penetration welds. All four tests demonstrated that the RBS connections without continuity plates developed a total interstory drift angle greater than 0.04 radians and met the requirements for special moment frames.

Determination of the load - displacement curve of moment resisting steel frames under horizontal loading

Seismic resistant steel frames are very common in regions of high seismic risk due to their excellent characteristics in terms of strength and ductility. For the evaluation of the total ductility, various methods have been proposed in the bibliography. In this paper a method is proposed for the evaluation of the total ductility in steel structures, which takes into account the exact form of the moment–rotation curve, including possible softening branches. In the above method, the strength degradation due to second order phenomena is also taken into account. The numerical algorithm presented in the paper is based on the background of nonconvex optimization theory. Numerical examples demonstrate the potential of the proposed method.