Earthquake Engineering & Structural Dynamics最新文献

Equivalent-lateral-force (ELF) procedure of seismic design considers accidental torsion by applying the design lateral force profile at an offset equal to accidental eccentricity from the CM. This paper evaluates the required accidental eccentricity in a median sense to account for the torsional ground motion, arguably the most dominant contributor of accidental torsion. The proposed recommendation of accidental eccentricity is based on the analysis of a wide range of one-storey torsionally coupled buildings subject to a suite of seismic events comprising the recorded orthogonal pair of horizontal accelerograms and the recorded torsional accelerogram. Demands from the simultaneous incidence of horizontal pair and torsional ground motions are met with those from the base shear of bidirectional horizontal excitations applied conforming to the required accidental eccentricity. The resulting accidental eccentricity depends on the triplet of uncoupled horizontal and torsional periods if the natural eccentricities are small, and otherwise, contingent on the natural eccentricities as well. Further, accidental eccentricity is observed to vary linearly with the radius of gyration beyond a threshold. A system with a threshold radius of gyration is defined as the reference system. Accidental eccentricity of any system with an arbitrary radius of gyration may be obtained using an amplification or deamplification of that recommended for the reference system. The proposal also considers all possible directionality of the horizontal pair given the same recorded torsional accelerogram. One example is also included, demonstrating the computation of system properties that are required to implement the proposed recommendation of accidental eccentricity in a multistorey building.

The study of unbonded post-tensioned (PT) bridge piers continues to gain momentum, as they can produce self-centering lateral force behavior with limited structural damage; however, little attention has been given to the dynamic responses of these controlled rocking systems. This paper presents an experimental study to investigate the motion pattern and assess the seismic performance of unbonded post-tensioned reinforced concrete (PRC) rocking bridge piers under uni- and bi-directional earthquake excitation. A conventional PRC pier and two improved versions with end segments enhanced, respectively, by a steel tube and ultra-high performance concrete (UHPC) were investigated through shaking table tests. The experimental outcomes highlighted the potential limitations of the two enhanced strategies in terms of damage-tolerance and rotation-dominance. Tests also revealed that the bi-directional displacement of PRC piers can be estimated from the individual uniaxial responses using the square root of the sum of the squares (SRSS) rule. In contrast, the force responses are overestimated by SRSS. Moreover, it has been observed that PRC piers are characterized by a three-dimensional (3D) wobbling motion with a contact region around the circular base instead of the sudden point impact during in-plane rocking. An analytical model is presented for the 3D rigid motion of PRC piers subjected to bi-directional earthquakes, which accounts for variations in the contact region at the pier-to-footing interface and relevant energy loss. The model's predicted responses aligned closely with the rotation-induced results derived from experimental data, provided the interface's contact properties were properly calibrated. The findings and results provide significant insights into the seismic response of PRC rocking piers, as well as further refinement of damage-tolerant solutions.

Socket connections play a pivotal role in accelerating construction and improving bridges’ resilience in seismic-prone regions. However, current design guidelines for reinforced concrete (RC) column-drilled shaft socket connections (CDSSCs) may inadequately account for the required shaft transverse reinforcement (STR). This study proposes an improved design method to estimate the hoop tension demand and capacity of shafts and determine the optimal spacing of STR. The proposed method is validated through quasi-static cyclic tests conducted on five CDSSCs with varying axial loads and column configurations. The tests highlighted different failure modes, including plastic hinges at the column bases, severe shaft cracking, debonding at the shaft-steel corrugated tube interface, and eventual shaft failure. The study further highlighted the response of CDSSCs by analyzing the deformation patterns, hysteretic behavior, and shaft reinforcement strains. Finite element (FE) models were developed in ABAQUS to replicate the experimental results, including force-drift responses, local responses, and failure modes. The validated ABAQUS models were used to perform a numerical parametric analysis by varying the STR spacing. For increasing STR spacings, the failure mode of the CDSSC progressively transitions from column to shaft failure, while the force transfer mechanism transitions from bending-dominated action to prying-dominated action. The results confirmed the effectiveness of the proposed method in controlling the failure modes of CDSSCs and designing the STR spacing.

This work evaluates how the dynamic response of the tuned mass damper (TMD) systems changes following the insertion of suitable displacement limiters. The systems, pounding tuned mass damper (PTMD), use the tuned mass to absorb the kinetic energy from the main system and dissipate it through the TMD damper and the impacts with the bumpers. Through numerical analyses, an optimal bumper design procedure is introduced; the effectiveness of the PTMD systems subjected to harmonic excitations at the base is evaluated, both for conventional and unconventional mass ratios; it is evaluated under which conditions the PTMD systems are more effective than the TMD systems; finally, the robustness of these systems to both TMD and bumpers parameters is investigated. The main results obtained have shown that (i) inserting bumpers to an optimally designed TMD does not lead to a more effective mitigation system; (ii) in those cases where optimally realizing a TMD can be complicated, or there are design constraints, the insertion of bumpers can bring significant increases in effectiveness; (iii) all the systems analyzed have shown an increase in effectiveness as the mass ratio of the TMD increases, up to a critical mass ratio after which losses in effectiveness are recorded; (iv) the analyses on the robustness of the PTMD systems have shown that such systems have good robustness both to TMD and bumpers parameters, highlighting how the parameter to which such systems are most sensitive are the distance between the auxiliary mass of the TMD and the bumpers.

Prior studies have demonstrated that walls implementing unbonded post-tensioned (PT) tendons can provide an effective solution to achieve a low-damage design objective. The wall-to-floor connection is crucial for the floor to achieve the low-damage performance requirements, and wall-to-floor interaction can also alter the lateral load transfer and overstrength actions that develop in the system. To validate low-damage concepts and connection detailing, a two-storey PT concrete wall building with both flexible and isolated wall-to-floor connection designs was recently subjected to shake-table tests. The design of the flexible connections aimed to transfer lateral loads while accommodating wall uplift with a link slab or composite floor. The isolated connections were designed to decouple the floor from the uplift and rotation of the wall to minimise the damage to the floor while transferring forces in the horizontal direction. The behaviour of these wall-to-floor connections was investigated in this paper with consideration of several performance criteria. Key objectives of this investigation of the two wall-to-floor connections included: (1) summarise the observed performance and damage states; (2) quantify the deformation responses; and (3) investigate the force transfer and acceleration responses. Test results confirmed that both the flexible and isolated connections effectively addressed deformation compatibility in the system. The flexible connection primarily accommodated wall uplift by developing narrow cracks that were distributed within the floor. The isolated connection allowed lateral load transfer without imposing deformations on the floor. The acceleration responses of the two connections exhibited different trends. The integral design of the flexible connection ensured that forces were fully transferred from the wall to the floor with consistent acceleration responses, while the isolated connection partially released the transfer mechanism, with only horizontal and vertical accelerations with low-frequency components transmitted through the connection.