Riccardo Zandonini

Experimental analysis and modelling of semi-rigid steel joints under cyclic reversal loading

Abstract This paper reports on the first phase of a research project aimed at developing simple design criteria for semi-rigid steel frames in seismic zones. The experimental phase comprised of two series of tests on beam-to-column joints under cyclic reversal loading. The evaluation of the test results first allowed the influence of the loading history to be investigated and the main stiffness and strength parameters to be identified, which define the cyclic response of the connection. A simple prediction model was then developed and proposed, which enables satisfactory approximation of the joint response for use in numerical analysis.

A reliability-based bridge management concept

Since 2004, the Autonomous Province of Trento, Italy, has adopted a Bridge Management System entirely based on reliability concepts. The system operates on the web, and includes sections for (1) condition state evaluation, (2) safety assessment, and (3) prioritization. Condition appraisal is based on visual inspections, and acknowledges the general rules of the AASHTO Commonly Recognized Standard Element system. Normally, the system conservatively estimates the prior reliability of each bridge, based on the sole inspection data. Where the condition of the bridge gives cause for concern, its reliability is evaluated in a more formal manner using multi-step procedures of increasing refinement. Decision-making is driven by a principle whereby priority is given to those actions that, within a certain budget, will minimize the risk of occurrence of an unacceptable event in the whole network. In this paper, the operation of the system is illustrated, with the support of a number of practical cases.

Ductile End Connections for Glulam Beams

Ductility, which is the capability of a structure to deform significantly beyond the elastic limit without brittle failure, is a fundamental property which can be an important requirement in many instances. In particular, the behaviour of structures under seismic actions depends on the capacity to withstand large displacements in the plastic field without reaching the collapse. Wood suffers from the unfavourable material characteristic that exhibits no (tension) and limited (compression) post-elastic deformation capacity. Therefore timber structures rely on steel dowel-type connections to provide ductility and energy dissipation. In general, good performance can be achieved by light timber structures with a large amount of steel connectors, designed to favour steel yielding as the governing mechanism. For heavy timber structures, because of the lower redundancy of the structure, a more “engineered” joint design is needed to ensure a safe performance during seismic events. The research reported in the present paper has been devoted to the investigation of an innovative steel-to-timber joint suitable for different joint configurations within a frame, where a timber element is connected to a steel stub by means of an end-plate and glued-in steel rods. The proposed system has been investigated by means of numerical models and experimental tests, in order to determine strength values and moment-rotation relationships of the joint. Some interesting conclusions can already be drawn from the available experimental tests, suggesting a possible full implementation of such techniques in seismic resistant timber structures, which is the ultimate goal of the research.

A hysteretic connection element and its applications

Abstract A hysteretic connection element for the simulation of hysteretic responses of connections is formulated and implemented in the non-linear finite element program DRAIN-3DX. In the formulation of the element, both stiffness-and-strength degradation and pinching are expressed as functions of damage state variables; meanwhile, damage is monitored and failure is detected by means of a damage index. In the implementation of the element, an automatic event definition algorithm is developed and an event-to-event solution scheme is followed. The element is applied to the simulation of hysteretic responses of unstiffened extended end plate connections, web panels, joints and frame substructures subject to cyclic reversal loading. Simulations are in good agreement with experimental data in terms of load-deformation relationship, strength, stiffness, and energy dissipation.

Cyclic Behavior of Headed Stud Shear Connectors

Three series of pull-push specimens with 16 mm and 22 mm diameter headed stud shear connectors were built and tested as part of a general investigation on seismic design of steel-concrete composite beams with full and partial shear connection. To assess the shear connector performances from a seismic and damage standpoint, pullpush specimens have been exposed to series of variable, random and constant reversed slips. Main results are commented upon and evaluated in terms of yielding and maximum shear strength capacity as well as ultimate slip ductility. A comparison between experimental and prediction strengths derived by relevant design code provisions provides an estimate of their accuracy. Finally, some low-cycle fatigue models are investigated to establish damage limit domains and fatigue life relationships for headed studs.

On estimating the accuracy of monitoring methods using Bayesian error propagation technique

This paper illustrates an application of Bayesian logic to monitoring data analysis and structural condition state inference. The case study is a 260 m long cable-stayed bridge spanning the Adige River 10 km north of the town of Trento, Italy. This is a statically indeterminate structure, having a composite steel-concrete deck, supported by 12 stay cables. Structural redundancy, possible relaxation losses and an as-built condition differing from design, suggest that long-term load redistribution between cables can be expected. To monitor load redistribution, the owner decided to install a monitoring system which combines built-on-site elasto-magnetic and fiber-optic sensors. In this note, we discuss a rational way to improve the accuracy of the load estimate from the EM sensors taking advantage of the FOS information. More specifically, we use a multi-sensor Bayesian data fusion approach which combines the information from the two sensing systems with the prior knowledge, including design information and the outcomes of laboratory calibration. Using the data acquired to date, we demonstrate that combining the two measurements allows a more accurate estimate of the cable load, to better than 50 kN.

Fusion of monitoring data from cable-stayed bridge

This contribution illustrates an application of Bayesian logic to monitoring data analysis and structural condition state inference. The case study is a cable-stayed bridge 260 m long spanning the Adige River ten kilometers north of the town of Trento, Italy. It is a statically indeterminate structure, consisting of a steel-concrete composite deck, supported by 12 stay cables. Structural redundancy, possible relaxation losses and an as-built condition differing from design, suggest that longterm load redistribution between cables can be expected. To monitor load redistribution, the owner decided to install a monitoring system that combines built-on-site elasto-magnetic and fiber-optic sensors. In this article, we discuss a rational way to improve the accuracy of the load variation, estimated using the elasto-magnetic sensors, taking advantage of the fiber-optic sensors information. More specifically, we use a multi-sensor Bayesian data fusion approach, which combines the information from the two sensing systems with the prior knowledge including design information and outcomes of laboratory calibration. Using the data acquired to date, we demonstrate that combining the two measurements allows a more accurate estimate of the cable load, to better than 50 kN.

Sensor Fusion on Structural Monitoring Data Analysis: Application to a Cable-Stayed Bridge

This paper illustrates an application of Bayesian logic to monitoring data analysis and structural condition state inference. The case study is a 260 m long cable-stayed bridge spanning the Adige River 10 km north of the town of Trento, Italy. This is a statically indeterminate structure, having a composite steel-concrete deck, supported by 12 stay cables. Structural redundancy, possible relaxation losses and an as-built condition differing from design, suggest that long-term load redistribution between cables can be expected. To monitor load redistribution, the owner decided to install a monitoring system which combines built-on-site elasto-magnetic and fiber-optic sensors. In this note, we discuss a rational way to improve the accuracy of the load estimate from the EM sensors taking advantage of the FOS information. More specifically, we use a multi-sensor Bayesian data fusion approach which combines the information from the two sensing systems with the prior knowledge, including design information and the outcomes of laboratory calibration. Using the data acquired to date, we demonstrate that combining the two measurements allows a more accurate estimate of the cable load, to better than 50 kN.

Seismic Behavior of a 3D Full-Scale Steel-Concrete Composite Moment Resisting Frame Structure

This paper shows the feasibility of composite MR frame structures with partially encased columns and partial strength beam-to-column joints to provide strength and ductility. In detail, energy dissipation is concentrated both in column web panels which are not surrounded by concrete and in composite beam-to-column connections. A full-scale two-storey composite building was used to validate the system performance of composite MR frames with partial strength joints. The frame structure was subjected to pseudo-dynamic tests in order to simulate the structural response under ground motions. The ground motion for 10 % chance of exceedence in 10 years earthquake hazard caused minor damage while the one for 2 % chance of exceedence in 10 years earthquake hazard entailed column web panel yielding, connection yielding and plastic hinging at column base joints. An earthquake level chosen to approach the collapse limit state induced more damage and was accompanied by further column web panel yielding, connection yielding and inelastic phenomena at column base joints without local buckling. Successively, the structure was subjected to a final quasi-static cyclic test with interstory drift ratios over 4.6 %. Moreover, test offered additional opportunities to validate the performance of simulation FE models. Exploiting inelastic static pushover and time-history analysis procedures, behavior factors, design overstrength factors and the ductility demand of the structure were estimated.

Quasi-Static Cyclic and Pseudo-Dynamic Tests on Composite Substructures with Softening Behaviour

ABSTRACT Six full-scale steel-concrete composite substructures, part of a moment-resisting rigid frame were built and tested both in a quasi-static cyclic and a pseudo-dynamic fashion as part of an investigation on aseismic design of composite systems. The specimens embodied two composite beams with full shear connection and four companion beams with two different degrees of partial shear connection, all with exterior rigid joints. The tests were conducted in a low-cycle high amplitude regime. Thereby, stiffness, strength, ductility and energy consumption properties of substructures under reversed cyclic displacements as well as the effects of local buckling on the properties of beam-to-column joints were analysed. Main test data are commented upon and substructure seismic performances are assessed. Finally, a comparison between experimental and design strength capacity predicted by the relevant European code is provided.