Three-span Structure Research Articles

Seismic performance and fragility of two-story and three-span underground structures using a random forest model and a new damage description method

This paper proposes a new method for evaluating the seismic performance and fragility of large underground structures. A typical underground subway station consisting of a two-story and three-span structure was used as the research subject. Considering the variation of sites and the uncertainty of input ground motions, we developed a finite element model of a nonlinear dynamic soil-underground structure interaction system. Based on the incremental dynamic analysis method, the nonlinear seismic responses of the subway station structure were calculated for 900 cases. Python (software) was used to accelerate the processing of the large number of numerical simulation data. Based on the seismic damage characteristics of an underground structure, this paper proposes a new concept of average seismic damage value to evaluate the damage condition of the underground structure to overcome the inadequacies induced by an expert’s intuitive judgment. Meanwhile, the random forest prediction model was adopted to predict the seismic performance levels (SPLs) of the underground structure, and a non-parametric test was performed to verify the correlation between the degree of seismic damage and the inter-story drift ratios (IDR) of the large underground structure. This proved that the IDR could describe the seismic damage of shallow-buried underground structures; we advanced a precise quantification system of the SPL for shallow-buried subway station structures with two-story and three-span using probability statistics. The peak ground velocity (PGV) is more suitable than the peak ground acceleration (PGA) for use as the seismic intensity measure (IM) for large underground structures when the stiffness of the soil foundation becomes soft. In addition, the seismic fragility curves of the shallow-buried subway station structure were constructed and analyzed using the developed quantification system for the SPL.

TESTING OF BRIDGES DAMAGED AS A RESULT OF COMBAT ACTIONS

The work examines the application of methods of static and dynamic testing of bridges damaged as a result of hostilities. Penetration by projectiles and damage by explosions of structural elements, in addition to obvious damage, also form a series of hidden defects, the determination of which according to norms and regulatory documents is regulated to be carried out by means of tests with calculated loads. For testing bridges in accordance with the requirements of construction standards and regulatory documents, the equipment developed by the author of the article was used for digital registration and processing of signals of acoustic emission and mechanical vibrations. The results of static tests of three span overpasses made of precast concrete with a length of 63.20 m along the street are presented. Kvitneva in the city of Chernihiv and a four-span pedestrian bridge with a length of 263.1 m across the Desna River in the park zone of the city of Chernihiv. The peculiarities of the application of the acoustic emission method for determining the state of the span structures of the bridge during static tests with step loading are considered. During the analysis of the results of the dynamic tests of the pedestrian bridge, the results of the application of wavelet analysis were translated to reveal the characteristics of the oscillations of a non-separable steel three-span structure that received dynamic load impulses and determine the natural frequency of oscillations of the span structures. The results of the work are recommended for use during the examination and testing of bridges, the girder structures of which have hidden defects and damage, as well as for constant monitoring of the structures.

Refurbishment of Middleton Road Bridge, Oldham, UK

Middleton Road Bridge carries the dual carriageway A627 Oldham Way over the A669 Middleton Road, to the west of Oldham town centre in Greater Manchester, UK. The bridge, built in 1980, is a three-span structure with spans of 16.859 m, 24.077 m and 15.479 m, with a skew of approximately 35°. The precast prestressed concrete beam suspended centre span is supported on half-joints built into cantilevers from the in situ concrete side-spans. There are spread foundations with bankseat abutments and circular columns that are pinned to the deck through pot bearings. The bridge experienced significant unplanned movement, together with deterioration to joints, concrete spalling and reinforcement corrosion. Of the schemes considered by Transport for Greater Manchester, refurbishment of the bridge was ranked as the highest priority in 2016. This paper describes the likely original design assumptions, the observed defects, investigations and diagnoses of the causes of these defects, remedial and refurbishment works design, constraints to the works, construction issues and their resolution. The cost of the refurbishment works was £1 312 957.14 and the work was completed in November 2018.

Evaluation of Different Monitoring Techniques During Damage Infliction on Structures

This paper presents a case study of a post-tensioned reinforced concrete bridge built in the 1970s which underwent a two month monitoring period prior to its demolition. The 62 m long two-lane bridge was to be replaced by a newer construction designed for higher traffic loads and was thus available for in-situ trials once it had been closed to traffic. The monitoring started in February 2016 to observe the three-span structure in its original state when excited by ambient and vehicle-induced vibrations. Initial construction works around the sloping abutment and the pier foundations, such as pile driving and extension of the embankment, started at the end of March, followed by the closure to traffic and the removal of the asphalt pavement. Over the next few weeks, the bridge saw three damage scenarios induced in the following order: 1. Six out of sixteen tension cables were severed above one of the piers; 2. Expansive mortar was filled into boreholes in the deck; 3. Expansive mortar was filled into boreholes in one of the piers to induce cracking. The bridge was equipped with accelerometers, inclination sensors and fibre-optic strain gauges that continuously monitored the structure’s condition. For safety reasons, the sensors in direct vicinity of the damage points were gradually moved to other parts of the bridge or dismantled completely in the course of the damage infliction. The aim of the monitoring was to assess the detectability of the structural weakening using a variety of measurement techniques and to see what role data quality, sensor positioning and auxiliary information plays in reliably diagnosing the extent of the damage or defining an alarm level. Different ways of post-processing the data were examined to see what information can be gained without having to create a numerical model of the structure when insufficient design documents are available.

Design and construction of a railway flyover at Hitchin, UK

A new 837 m long elevated railway has been built at Hitchin in the UK to carry trains between London and Cambridge over the East Coast Main Line. It relieves the main bottleneck at the junction where Cambridge line trains cross the East Coast route on a flat junction. The project involved the design and construction of a 29-span viaduct made of a steel–concrete composite deck, which is effectively composed of 15 jointed structures. Twelve of these are made of two continuous 30 m spans, two structures are made of single, simply supported spans and the remaining length is a continuous three-span structure with a maximum central span of 60 m that crosses the railway at a skew angle of more than 60°. The 425 m curved plan radius alignment was a design challenge as significant torsional effects are caused by the plan curvature, the eccentricity of applied vertical actions, the centrifugal effects and the wind pressures acting on the trains. Steel erection started with the main railway spans, a process that took three overnight possessions due to the curvature, the heavy skew and the geometry of the girders. This paper describes the critical design aspects and the main construction operations of the flyover.

Concrete creep effects during bridge span construction using cantilever concreting technology

A characteristic feature of many long-span cantilever prestressed concrete bridges are excessive deflections of their spans due to the rheological processes in the concrete and in the prestressing steel. Such bridges are subject to monitoring during which geodetic surveys are usually conducted. The latter reveal changes in the deflection curves of the spans. In this paper span displacements resulting from concrete creep are analysed. A specific situation occurring when the span static scheme is changed from the cantilever (assembly stage) to continuous beam (exploitation stage) is considered. Assuming a regular three-span structure, a general solution to the problem is obtained for the following bridge parameters: dead load, span length, and the variable concrete creep index. The proposed algorithm is used in calculation examples in which different creep index distributions along the cantilevers are assumed. The results of the analyses are compared with the behaviour of a monitored existing bridge of this type. The analyses presented in this paper can be useful for the design of spans and the assessment of the safety of such bridges which are in service.

Procurement, design and construction of the Clyde Arc, Glasgow

The design and construction of the Clyde Arc has created a new landmark structure on the River Clyde waterfront in Glasgow. The construction of the £20·3 million project commenced in May 2005 and was completed in September 2006. The bridge is a three-span structure, the central span comprising a tied bow string arch with a single steel diamond-shaped arch rib spanning the long diagonal of the span. The main deck consists of a composite steel ladder beam arrangement with two longitudinal plate girders and cross girders at 4 m centres acting compositely with a reinforced concrete deck. The centre span is supported directly from 14 hanger bars, each 110 mm in diameter. The lower hanger connections are attached to outriggers from the main longitudinal girders, which are connected longitudinally with tubular members. The back spans are supported at the pier cross girders and are integral with the reinforced concrete abutments, which are in turn supported on reinforced concrete piles of small diameter. The centre span is supported on tubular steel piles of large diameter, within the river. This paper describes the procurement, design and construction of this structure.

Examination of Level of Analysis Accuracy for Curved I-Girder Bridges through Comparisons to Field Data

To evaluate the accuracy of different levels of analysis used to predict horizontally curved steel I-girder bridge response, a field test was performed on a three-span structure. Collected strain data were reduced to determine girder vertical and bottom flange lateral bending moments. Experimental moments were compared to numerical moments obtained from three commonly employed levels of analysis. Level 1 analysis includes two manual calculation methods: a line girder analysis method described in the AASHTO Guide Specification for Horizontally Curved Highway Bridges, and the V-load method. Grillage models represent Level 2 and were created using three commercially available computer programs: SAP2000, MDX, and DESCUS. Level 3 consists of three-dimensional 3D finite element models created using SAP2000 and the BSDI 3D system. Responses obtained from each level are compared and discussed for a single radial cross section of the structure, and the compared results involve truck loads and placement schemes that do not represent those used for bridge design. The field test and numerical data presented are used solely to determine the accuracy of each level of analysis for predicting structure response to a specific live load at a specific cross section. Results showed that Level 2 and Level 3 analyses predict girder vertical bending moment distributions more accurately than Level 1 analyses throughout the tested cross section. The comparisons indicate that Level 3 girder vertical bending moment distributions offered no appreciable increase in accuracy over Level 2 analyses. The study also indicates that both Level 1 and Level 3 analyses provide bottom flange lateral bending moment distributions that do not correlate well with field test results for the studied bridge cross section.

Continuous Composite-Bridge Model Tests

The results of ultimate-load tests on two continuous-span composite slab-girder bridge models are presented. One of the models was a three-girder two-span structure and the other was a three-girder three-span structure. Both models were tested to failure with a single concentrated load applied over the center girder. The purpose of the tests was to determine the variations in both the distribution of moment throughout the structures and the effective widths of slab acting with each girder as the load is increased to failure. The experimental results are compared with an existing analytical procedure and a major conclusion is that the analytical procedure may be used to conservatively model actual bridge structures up to failure loads. In addition, it is concluded that effective widths and distribution factors at failure loads are significantly different from values obtained at service loads. The implications of the latter observations in bridge design are discussed.