Suspended Span Research Articles

Experimental and simulation study of pounding tuned mass damper on jumper flow induced vibration

Subsea jumpers carrying gas-liquid mixed flows can experience flow-induced vibration (FIV), potentially shortening their service life. The pounding tuned mass damper (PTMD), impact at the viscoelastic boundary can be used to dissipate energy. This paper focuses on a rigid m-shaped jumper to evaluate the specific damping effects of PTMD on the jumper under gas-liquid flow. Three PTMD configurations with significant damping effects are tailored based on the natural frequency of the jumper. Vibration tests are carried out to assess the damping effectiveness of each configuration, and the most effective PTMD is selected. Subsequently, the damping efficacy of PTMD on FIV within the jumper under varying flow conditions is investigated using both experimental methods and numerical simulations (VOF and FIS model). The results show that PTMD has obvious damping effects on free vibration and the main frequency and high-frequency jumper vibrations caused by FIV. Subsequent to the installation of PTMD, a substantial reduction in displacement has been observed across all components of the jumper. The suspension span exhibits the most pronounced decrease, exceeding 60%, while the displacement at the elbow joint is reduced by over 40%.

Dynamic response of asymmetric suspended structure subjected to random wind excitation

SummarySuspended structures, regarded as the expression of structural beauty, have attracted the focus of many architects and engineers. With the complexity of dynamic responses of the asymmetric suspended structures subjected to the random alongside wind excitation, an innovative method was proposed through combining the finite element method (FEM), the complex mode method (CMM), the pseudo excitation method (PEM), and the quadratic decomposition method (QDM) of frequency response function. The method could obtain unified closed‐form solutions of spectral moment and variance of node displacement and velocity and acceleration of asymmetric structures and its correctness was verified by existing numerical approaches. The proposed method is applicable to the random wind‐induced vibration response analysis of diverse linear complex structures. Notably, its efficacy lies in its circumvention of numerical integration, endowing it with high computational efficiency and accuracy. Extended comparative studies and discussion were also performed on effect of suspended span and comparisons of normal framed structure and symmetry structure. The results showed that the suspended span presented positive relation to horizontal displacement and inverse tendency to horizontal acceleration of the whole structure and vertical and horizontal acceleration of the columns near to suspended part should also be considered in engineering design.

Calculation and prediction of suspended span caused by erosion of deep water submarine pipelines

Submarine pipelines can be divided into three types based on their laying status: pipelines laid flat on the seabed, pipelines without buried, and pipelines buried in shallow trenches. In addition, there is also a suspended span state caused by waves and currents erosion. The four laying states of submarine pipelines indicate that the seabed, as the foundation supporting the pipeline, must provide sufficient support to ensure the stability of the pipeline. This article studies the erosion span data of existing pipelines, evaluates and predicts the pipeline span state through theoretical calculation and analysis, and then uses numerical simulation calculation methods to predict the pipeline span depth, and compares and verifies it with measured data.

Torsional Optical Fiber Stress Analysis and Vortex-Induced Vibration Study of Three-Core Submarine Cable

Due to current scouring, submarine cables are prone to be exposed, suspended, and even vortex-induced vibration, which is not conducive to the safe operation of the power grid. In this contribution, the finite element simulation model of a 35 kV three-core optical fiber composite submarine cable with a suspended span length of 9.5 m is established. The natural frequency of the model is obtained through modal analysis. Then the vortex-induced vibration is simulated by the fluid–structure coupling method, and the stress distribution and change law of the torsional optical fiber is extracted. The results show that in the submarine cable, there appears to be a beating vibration and locking phenomena respectively, under two flow velocities. The transverse vibration amplitude of the latter increases significantly due to a resonance state. When the flow direction is perpendicular to the submarine cable, the stress distribution of the torsional optical fiber at the initial moment and at the 1/2 T moment of a vibration cycle approximately represents a mirror image relationship. In addition, the frequency of the stress change is the same as the frequency of the vortex-induced vibration, which can judge whether the vortex-induced vibration occurs. Moreover, the vortex-induced vibration range can be determined by the maximum stress change location.

Analytical Study on the Random Seismic Responses of an Asymmetrical Suspension Structure

An asymmetrical suspension structure, without vertical column support and without supplying the flexibility of spatial arrangement, is more sensitive to ground movement. The structural responses of an asymmetrical suspension structure subjected to Clough–Penzien spectrum excitation were analytically investigated in this study. First, the governing equation was decoupled into an independent state equation in generalized coordinates through the real mode decomposition method and by creatively combining it with finite element methods to acquire modal coefficients. Through the pseudo excitation method (PEM), the frequent domain solution of the dynamic response was acquired, and its power spectrum density function was then quadratically decomposed to obtain its corresponding 0–2-order spectral moments. A practical case study was performed to verify the high accuracy and computational efficiency of the proposed closed-form solution comparative to the traditional PEM. Finally, an extended analysis of the effect of the suspended span and comparisons to a normal framed structure and symmetrical suspension structures were carried out. The analysis results indicate that the larger suspended span could consume more seismic energy and result in smaller horizontal displacement and acceleration. Moreover, the comparison results also point out that the existence of the suspension part showed better seismic energy dissipation capacity compared to the normal framed structure, and two symmetrical suspension parts also performed better than a single asymmetrical part in seismic energy dissipation.

Experimental and numerical investigation on transverse impact resistance behaviour of pipe-in-pipe submarine pipelines after service time

The transverse impact resistance behaviour of pipe-in-pipe submarine pipelines after 15 years of service is studied experimentally and numerically. From drop hammer impact tests of 4 full-scale specimens, the influence of specimens’ span, corrosion and dent defect on the transverse impact resistance is studied in terms of failure mode, impact force-time history curves, displacement-time history curves, strain-time history curves and impact force-displacement curves. The experimental results indicate that the dynamic failure process consists of four stages, including primary vibration stage, secondary vibration stage, stable stage and unloading stage. As the suspension span of the specimen increases, the primary failure mode changes from local indentation to global bending deformation. The corrosion and the dent defect impair the impact resistance. Finite element (FE) models are then established and verified through comparison with experimental results. Numerical analyses indicate that the total impact energy is mainly dissipated by the outer pipe and the inner pipe according to the energy dissipation analysis for each component of the pipe-in-pipe specimens under transverse impact load. Parametric study is implemented finally to disclose the influence of the dimensions of pre-existing corrosion and dent defect on the transverse impact behavior of pipe-in-pipe submarine pipelines.

Decommissioning of the A14 Huntingdon Railway Viaduct, Cambridgeshire

This paper discusses the demolition of the central suspended span of the Huntingdon Railway Viaduct, which crosses the East Coast Main Line on the west side of the Cambridgeshire town. The structure became redundant in December 2019 when a new offline section of the A14 was opened to the south of the town as part of a National Highways improvement scheme.

Rotating characteristics and stability analysis of unsymmetrical magnetically suspended motor

The rotating characteristic and the stability analysis of unsymmetrical magnetically suspended motor (MSM) are investigated in the article. Firstly, the dynamic functions of unsymmetrical MSM with different moment of inertia ratios and suspension span ratios are developed. Based on the equation of radial rotation, the open-loop pole and the frequency response are analyzed, so relationships among critical whirling frequency, moment of inertia ratio and suspension span ratio are established. Moreover, relationships among rotating characteristic, moment of inertia ratio and suspension span ratio are investigated, and then the rotation stability criterion of unsymmetrical MSM based on dual-frequency bode diagram is developed. Finally, the results prove that the proposed rotation analysis method is a potential way to analyze rotating characteristic of unsymmetrical MSM.

Research on Design and Construction Technology of Large Span T-Truss Suspension Beam

Urban subway construction is often in the lower part of the city center road, and there are many municipal pipelines and pipelines in the lower part of the road. Because it involves the life of the surrounding residents, it is difficult to move and change. In the open excavation of foundation pit, the whole suspension construction measures are often used to solve this problem. Within the excavation area of the Yingmentan Station passageway of Lanzhou Rail Transit Line 1, there is a steel pipe municipal water supply pipeline. This municipal water supply pipeline needs integral suspension protection, with a suspension span of 22.5m. The design adopts T-shaped truss beams for overall suspension. This paper uses T-shaped beam design and force analysis research. Provide reference for similar projects.

Research on Non-Pillar Coal Mining for Thick and Hard Conglomerate Roof

This article introduces a new non-pillar coal mining technology (i.e., Gob-side Entry Retaining by Roof Cutting (GERRC)) under the condition of thick and hard roofs. First, we theoretically analyzed the solution to the large suspension span of the thick and hard roof in coal mining. Three-Zone pre-split blasting design in non-pillar coal mining for thick and hard roofs was proposed, based on the principles of rock mechanics. After field experiments, the technology was successfully applied to the non-pillar coal mining of a huge thick conglomerate roof. This research supplements the non-pillar mining technology system. The proposed technologies and methods have strong applicability and have certain guiding significance for the safe and efficient mining of related coal mines.

Analytical study of thermal upheaval buckling for free spanning pipelines

Subsea pipelines with a free suspended span segment may be subject to upheaval buckling under high temperature, which may lead to a failure mode such as local buckling, fracture and fatigue. Mathematical models are established to study the upheaval buckling behaviour of subsea pipelines with a free span segment. Then, the accurate locations of the maxima of displacement and stress are obtained. The buckled configuration and the typical post-buckling behaviour and their dependence on free span length are analysed. Furthermore, a detailed analysis is presented for critical temperature difference, displacement amplitude and maximum axial compressive stress. Finally, the influence of touchdown on post-buckling behaviour during the process of upheaval buckling is discussed. The results show that the pipeline is prone to upheaval buckling when the free span length is large enough and the critical temperature difference decreases with increasing free span length. The displacement amplitude and the maximum stress within the span increase with the increase of the free span length before touchdown. However, after the pipeline touches the bottom of the free span, the maximum stress within the span decreases significantly compared to the case without touchdown, which becomes further smaller for smaller depth of the free span.

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.

Fragility‐Based Improvement of System Seismic Performance for Long‐Span Suspension Bridges

In this study, a procedure is developed to evaluate and improve the seismic performance of long‐span suspension bridges based on the performance objectives under the fragility function framework. A common type of suspension bridge in China was utilized in the proposed procedure, considering its approach structures according to earthquake damage experience and fortification criteria. Component‐level fragility curves were derived by probabilistic seismic demand models (PSDMs) using a set of nonlinear time‐history analyses that incorporated the related uncertainties such as earthquake motions and structural properties. In addition, one step that was covered was to pinpoint the capacity limit states of critical components including bearings, pylons, and columns. The stepwise improved seismic designs were proposed in terms of the component fragility results of the as‐built design. Results of the comparison of improved designs showed that the retrofit measure of the suspension span should be selected based on two attributes, i.e., displacement and force, and the restraint system of the approach bridges was a key factor affecting the reasonable damage sequence. Necessarily, from the comparison of different system vulnerability models, the mean values of earthquake intensity of system‐level fragility function developed by the composite damage state indices were used to assess the overall seismic performance of the suspension bridge. The results showed that compared to the absolutely serial and serial‐parallel assumptions, the defined composite damage indices incorporating the thought of component classification and structural relative importance between the main bridge and approach structures were necessary and were able to derive a good indicator of seismic performance assessment, hence validating the point that the different damage states were dominated by the seismic demands of different structures for the retrofitted bridges.

Coupling effects between wind and train transit induced fatigue damage in suspension bridges

Long-span steel suspension bridges develop significant vibrations under the effect of external time-variable loadings because their slenderness. This causes significant stresses variations that could induce fatigue problems in critical components of the bridge. The research outcome presented in this paper includes a fatigue analysis of a long suspension bridge with 3300 meters central suspended span under wind action and train transit. Special focus is made on the counterintuitive interaction effects between train and wind loads in terms of fatigue damage accumulation in the hanger ropes. In fact the coupling of the two actions is shown to have positive effects for some hangers in terms of damage accumulation. Fatigue damage is evaluated using a linear accumulation model (Palmgren-Miner rule), analyses are carried out in time domain by a three-dimensional non-linear finite element model of the bridge. Rational explanation regarding the above-mentioned counterintuitive behavior is given on the basis of the stress time histories obtained for pertinent hangers under the effects of wind and train as acting separately or simultaneously. The interaction between wind and train traffic loads can be critical for a some hanger ropes therefore interaction phenomena within loads should be considered in the design.

Overlying strata structural modeling and support applicability analysis for large mining-height stopes

After examining the roof strata movement pattern of fully mechanized mining (or caving) with large mining height, a roof structural model for large mining-height stopes was established based on their overlying rock structure; the overlying rock structure and movement pattern of these stopes were investigated; a method for determining the support working load and yield under "given deformation" and "limited deformation" states was proposed; the concept of immediate roof in mining operation with large mining height was modified; the roof control design criteria and support load calculation method for large mining-height stopes were established. The result indicates that increases in the mining height will largely increase the thickness of the immediate roof as well as the possibility of hard rock with large-span suspension top in the immediate roof. The key strata of the main roof having notable influences to stope strata behavior can be divided into two types of structures: a "single key stratum" structure and a "double key strata" structure. If the main roof was a "double key strata" structure, it will be important to prevent both threats like roof cutting or prop over yield in response to movement of the underlying key stratum, and the dynamic pressure impact to the stope in times of weighting of the overlying key stratum. Accurately determining the position, thickness and potential maximum suspended span of the suspension top was the key for the roof control design and support selection calculation for large mining-height stopes.

GUST RESPONSE ANALYSIS OF OVERHEAD TRANSMISSION LINES FOR INTERPRETATION OF WIND-INDUCED VIBRATIONS MEASURED IN THE FIELD

Several accidents occurred in bundle conductor overhead transmission lines due to large amplitude wind induced vibrations. In evaluating possible causes of these accidents and to develop appropriate counter measures, it is important to have a clear interpretation of the nature of vibrations which actually occurs in the field. This study is carried out to interpret large amplitude field measured wind induced vibrations based on gust response analysis of overhead transmission lines. Time average characteristics of field measured wind-induced vibrations have been discussed based on spectral analysis and time series acceleration. Eigenvalue analysis results of developed three dimensional finite element (FE) model of transmission lines has been discussed with dominant frequency of field measured response spectrum. Wind force has been modeled based on field measured characteristics of wind. Gust response of transmission lines has been evaluated by using developed finite element model of transmission lines and discussed with field measured vibrations. Results from field measured data analysis and eigenvalue analysis showed that cause of large amplitude vertical vibration does not happen due to resonance and galloping of transmission line-A. In case of transmission line-B, some events are found due to resonance and others events have a possibility of galloping as well as gust responses. Random peaks have been observed in time series acceleration which implies impulsive response and well confirmed with numerically obtained gust responses by using FE analysis. Suspension span are more prone in torsional response which are well confirmed with numerical results

Numerical investigation of local scour beneath a sagging subsea pipeline in steady currents

Two dimensional (2-D) numerical simulations are conducted to predict scour below the midsection of the suspended span of a pipeline that sags naturally into a scour pit. The deflection of the pipeline is calculated based on the suspension length (or span length) of the pipeline, which is predicted by an empirical formula for the length of the scour pit. The general properties of the scour process are investigated for various pipeline properties, pipeline embedment depths and Shields parameters. The effect of each of these parameters on pipeline sagging are combined into one non-dimensional sagging parameter. A touchdown time is defined as the time when the pipeline touches the bottom of the sand pit. Empirical formulae are proposed for predicting the final scour depth at touchdown and the time scale required for touchdown. It is found that the final sagging depth is a function of the sagging parameter and the Shields parameter, whilst the touchdown time is only a function of the sagging parameter. A formula is also developed for predicting the time history of scour depth prior to touchdown. Collectively, the empirical formulae and numerical simulations are found to be in reasonable agreement with an existing theoretical model available in the literature.

Strut-and-tie models for deteriorated reinforced concrete half-joints

A reinforced concrete half-joint bridge consists of suspended span dapped-end beams or a full-width deck supported on the nibs of abutments or adjacent beams. The design of their disturbed regions is traditionally performed by means of strut-and-tie modelling. The design provisions found in standards and codes can be used for the assessment of existing structures with minor adjustments. However, current documents provide limited guidance on the incorporation of deterioration aspects such as corrosion, insufficient anchorage lengths, and crack formation.Experiments performed on 12 half-joint beams demonstrated the effects of single defects, but synergistic effects were also found to exist and might lead to much higher reductions than expected from the sum of individual defects. These results were compared to different strut-and-tie models (STMs) and the application of STMs to achieve the highest lower bound estimate of the load carrying capacity is discussed.For the beams studied in the current work, the predictions based on codes and standards, combined with appropriate methods to incorporate deterioration effects, led to safe load bearing capacity estimates. However, the developed STMs seem to be, in some instances, unable to pick up alternative load paths that develop as soon as the capacity of a certain tie is reached. Hence the actual capacities might be higher than what is obtained from the STM calculations.

Allowable span length of submarine pipeline in shallow water

ABSTRACTBecause of the complex geological conditions of the seabed, submarine pipelines buried beneath the ocean floor become suspended over the seabed under the long-term scour of waves eroding the surrounding sediment. Further, most oil fields were built in offshore areas while the country was developing. This gives the waves seen in shallow water obvious nonlinear features, and the abnormal characteristics of these waves must be considered when calculating their hydrodynamic forces. Particularly under such conditions, these suspended spans of submarine pipelines are prone to damage caused by the action of the external environment load. Such damages and eventual failures may result not only in great property losses but also pollution of the marine environment. The span length of these areas is a key predictive factor in pipeline damages. Therefore, determining the allowable span length for these submarine pipelines will allow future projects to avoid or prevent damage from excessive suspended span lengths. Expressions of the hydrodynamic loads placed on suspended spans of pipeline were developed in this work based on the first-order approximate cnoidal wave theory and Morison equation. The formula for the allowable free span length was derived for the common forms of free spanning submarine pipeline based on the point where maximum bending stresses remain less than the material’s allowable stress. Finally, the allowable free span length of real-world pipelines was calculated for a subsea pipeline project in Bohai Bay. This research shows that, with consideration for the complicated marine environment, existing suspended spans are within allowable length limitations. However, continuing to limit the length of these submarine pipeline spans in the Nanpu oil field will require ongoing attention.

Waterloo Bridge – structural behaviour and strength

Waterloo Bridge, carrying the A301 road across the River Thames in London, was completed in 1942. It comprises twin multi-cell reinforced-concrete box girders of variable depth with connecting transverse slab, supported on caisson foundations. The paper describes the analysis and load assessment using modern techniques of a structure originally designed without the use of computers. The original articulation system incorporated stops to restrict longitudinal movement, and dynamic damping devices. The assessment has taken account of the actual behaviour of the structure determined from movement measurements. The centre suspended span is supported by hinge joints, which comprise steel roller bearings attached to concrete with pre-stressed vertical and diagonal bars. These bearings and their associated supports were subject to detailed analysis to determine their ultimate strength. The assessment has led to a much better understanding of bridge performance and residual life, which will enable the bridge owner to plan future maintenance interventions.