Conference Papers

A Parametric Study of Pedestrian Vertical Force Models for Dynamic Analysis of Footbridges

Paul Archbold et al. — Tue, 11 Sep 2012 04:55:33 PDT

Footbridge vibration has received much attention in recent years. However, stochastic models for crowd loading are not common, and estimation of crowd-induced vibration is typically done through enhancement factors applied to single pedestrian loading models. This work compares two such models, a moving force model and a spring-mass-damper model (SMD). Typical ranges for various pedestrian parameters are examined, and it is found that the pacing frequency has by far the greatest influence on bridge vibration response. It is also found that the magnitude of the response for pacing frequencies near the bridge natural frequency is lower for the SMD model, but otherwise the results prove similar. This suggests that moving SMD models may be more suitable than moving force models when the bridge natural frequency is in the critical frequency range.

The Response of a Footbridge to Pedestrians Carrying Additional Mass

Darragh O'Sullivan et al. — Tue, 11 Sep 2012 04:55:29 PDT

Footbridges with low natural frequency are susceptible to excessive vibration serviceability problems if the pedestrian pacing frequency matches the bridge natural frequency. Much research has been done into describing the response of a footbridge to single pedestrian loading. However, many pedestrians carry additional mass such as shopping bags and backpacks, and this has generally not been accounted for in previous research. This work examines this problem using an experimental bridge excited with many single pedestrian events, both with and without additional mass. The vertical acceleration response is measured and compared to moving force, moving mass, and moving spring-mass-damper models. The influence of the additional mass on the results is assessed. It is shown that current theoretical models do not provide an accurate description of the walking forces applied by a pedestrian traversing an excessively vibrating structure. When a pedestrian carries additional mass the response of the footbridge increases however the theoretical models overestimate this increase.

Estimating the Characteristic Vertical Response of a Flexible Footbridge Due to Crowd Loading

Joe Keogh et al. — Tue, 11 Sep 2012 03:55:22 PDT

The issue of excessive vibration of footbridges due to pedestrian loading is now well documented. Bridge vibrations produced from a crowd of pedestrians have been estimated by modifying the effect caused by a single pedestrian by an enhancement factor to take crowd synchronization into account. In this paper this approach is extended to account for the fact that all pedestrians will not have the same pacing frequencies, and the effects of distributions of pacing frequency and other parameters on the enhancement factor are investigated. It is shown that this more faithful representation of pedestrian crowd walking behaviour gives reduced vibration response compared to the fully homogenous crowd case. Based on these results, enhancement factors for predicting the response due to a crowd from the predicted accelerations of a single pedestrian are proposed. Further, the results are compared with published test results to indicate that the model is reasonable.

The Effect of Clusters within Crowds of Pedestrians on the Vertical Response of a Flexible Footbridge

Joe Keogh et al. — Tue, 11 Sep 2012 03:50:23 PDT

The issue of excessive vibrations of footbridges due to the passage of pedestrians has been well documented in the past decade. Despite this there still remains great uncertainty as to how to predict the acceleration response of a footbridge due to crowd loading. This paper investigates the vibration response of a flexible footbridge subjected to crowd loading. Using a statistical model which caters for the variability of pedestrians, the vibration response of the footbridge is obtained. In this work, the effect of social groups or clusters of pedestrians in a crowd is investigated. Herein a cluster is defined as two or more pedestrians walking together with the same velocity. The predictions of this model are compared to a model which uses only lone pedestrians walking within a crowd. None of the current design codes or guidelines considers the possibility of pedestrians walking together. The size of the clusters is found in literature to follow a Poisson distribution. In this paper variations of the probability of clusters appearing in the crowd are assessed. It is found that the response of a crowd with clusters present is similar to the predictions of the UK National Annex to Eurocode 1.

Reliability Analysis of Footbridge Serviceability Considering Crowd Loading

Joe Keogh et al. — Tue, 11 Sep 2012 03:10:33 PDT

The characteristic vertical response of flexible footbridges subjected to single pedestrian and crowd loading is examined in this paper. Typically, bridge vibrations produced from a crowd of pedestrians are estimated by using an enhancement factor applied to the effect caused by a single pedestrian. In this paper a moving force model is used in Monte Carlo simulations of a non-homogeneous sample of single pedestrians and crowds to estimate characteristic vertical vibration levels. Also in this work, statistical distributions of the bridge parameters are considered, these include flexural rigidity, mass and rotational stiffness at the supports. It was previously proven by the authors that the statistical range of pedestrian parameters, most notably the pacing frequency, has a significant effect on the bridge deck vibration. In this paper, probability of failure is calculated for ranges of pedestrian and bridge input parameters and it is found that the addition of statistical ranges for bridge parameters has only a small effect on the vertical acceleration response of the bridge deck. It reduced the probability of serviceability failure for a bridge with a natural frequency of 1.96 Hz and 2.2 Hz subjected to the loading of a characteristic single pedestrian.

Vertical Response of a Footbridge Subjected to Stocastic Crowd Loading

Joe Keogh — Tue, 11 Sep 2012 03:10:32 PDT

Characteristic Vertical Response of a Footbridge Due to Crowd Loading

Colin Caprani et al. — Tue, 11 Sep 2012 03:10:30 PDT

The characteristic vertical vibration of a flexible footbridge subject to crowd loading is examined in this paper. Typically, bridge vibrations produced from a crowd of pedestrians are estimated by using an enhancement factor applied to the effect caused by a single pedestrian. In this paper, a single pedestrian model, represented by a spring mass damper, which incorporates variables such as pedestrian mass and body stiffness, is used to calibrate a computationally efficient moving force model. This calibrated moving force model is further used in Monte Carlo simulations of non-homogenous crowds to estimate characteristic vertical vibration levels. Enhancement factors, which could be applied to simple single pedestrian moving force models in estimating the response due to a crowd are thus derived. Such enhancement factors are then compared to previously published values. It is found that the greatest difference between the spring mass damper and moving force models respectively occurs when the bridge frequency is at the mean crowd pacing frequency. For bridges with frequencies even slightly removed from this mean, moving force models appear adequate.

Incorporation of Life Cycle Models in determining Optimal Wind Energy Infrastructural Provision

Brendan Cleary et al. — Fri, 29 Jun 2012 06:44:22 PDT

The deployment of wind energy has grown rapidly over the last two decades with an average annual growth rate of more than 26% since 1990. During this period the development and innovation of wind turbines has resulted in continual growth in wind turbine size with output ranges of 10-15MW likely to be deployed by 2020. This increased output has a knock-on effect on the growth of rotor diameters and tower heights. Wind turbine towers are required to become taller, stronger and stiffer in order to carry the increased weight and associated structural loading. Consequently, the dimensions of the tower cross-sections must be increased which results in manufacturing and transportation difficulties as well as increased material costs. Thus, this paper focuses on the development of wind energy technology over the last two decades and the optimisation techniques cited in current literature. From this, a multi-objective optimisation problem is defined as maximising the structural performance of wind turbine towers while simultaneously reducing the life cycle costs and emissions associated with electricity generation from wind. A multi-objective optimisation model based on a harmony search algorithm is presented. This model is proposed to be developed further in order to determine a set of optimal combinations known as Pareto optimal solutions, which will allow a trade-off between the life cycle costs and emissions. Findings from the continuing research are envisaged to support the deployment of large scale wind turbines both onshore and offshore from structurally more promising, economically more competitive and environmentally greener towers.

Using Life Cycle Assessment to Compare Wind Energy Infrastructure

Brendan Cleary et al. — Tue, 12 Jun 2012 05:52:56 PDT

Given the need to significantly reduce greenhouse gas (GHG) emissions due to the production of electricity, countries worldwide are trying to develop and implement different energy saving strategies and technologies to mitigate global warming. A core part of achieving this is the development and implementation of renewable energy technologies such as wind.

This has resulted in the development and innovation of wind turbines with output ranges of 10-15MW likely to be deployed by 2020. This increased output has a knock on effect on the growth of rotor diameters and tower heights requiring the wind turbine system to be assessed from an economic, environmental and structural performance viewpoint. This has led to the proposal of using concrete as an alternative to the current preference of steel for wind turbine towers due to a number of limiting issues.

Thus, the main focus of this paper is to investigate and compare the life cycle emissions (LCE) of GHG of concrete relative to steel as a tower solution in order to identify a solution for both onshore and offshore facilities. The main findings indicated that the LCE for a wind turbine with a concrete tower range between 4-9% lower than its equivalent steel solution over a 40 year life cycle.

Water Savings and Rainwater Harvesting – Pilot Project in Ireland

Sean O'Hogain et al. — Fri, 20 Apr 2012 01:14:00 PDT

A pilot project to harvest rainwater was set up in Ireland in 2005 to examine the potential of using rainwater harvesting systems to replace treated mains water, for non-potable uses. The Project has two strands to it. The agricultural application assessed the feasibility of incorporating rainwater supply to supplement/replace mains or other water supplies for farms. The second strand involves rural water supply to domestic dwellings. Here the project installed rainwater harvesting and water conservation devices as part of a pilot project to assess the reduction in domestic demand. This paper will examine the water use recorded on both sites. It will present the findings of flow monitoring carried out on the agricultural site. Water savings will be presented in terms of rainwater volumes substituted for mains water, and in terms of economic savings, to the enduser and to the water producer. Water use will be compared with existing data available on water use on the farm. In the domestic situation, baseline results from non-rainwater harvesting houses monitored as part of the project will be compared with results from those fitted with rainwater harvesting. Water savings will be presented and discussed in terms of volume reduction in public water use and economic savings to user and producer.

The Operation of Hybrid Reed Bed and Willow Bed Combinations in Ireland - Zero Discharge and the Potential for no Monitoring of Domestic Applications of this Combination

Sean O'Hogain et al. — Thu, 19 Apr 2012 01:33:52 PDT

This paper will briefly trace the development of reed beds, the treatment mechanisms involved and the evolution of the more popular designs, with emphasis on the hybrid reed bed. It will also present a review of the concept of using willow beds to deal with waste water. It will examine the Danish guidelines. It will also review the application of willows to treat effluent from a hybrid reed bed system and the evolution of this system in Wales. The theory of willow bed treatment will also be discussed with particular emphasis on the factors that effect evapotranspiration. Two alternative designs for a willow soakaway will also be presented. The concept of a reed willow bed combination to treat municipal and domestic wastewater has been tested by the School Civil and Building Services Department of Dublin Institute of Technology, for the past number of years. Two sites have been tested in this eight year period, with promising results in the first. Based on this design a second installation was commissioned. This paper will present a case study of the first hybrid reed bed and willow bed system installed in Colecott, Co. Dublin, under the auspices of Fingal Co. Council. It will present design criteria. A brief discussion of the two year monitoring programme will be presented. The case study will also include a critique of the system and its operation. The paper will then describe the second reed and willow bed installation at Lynche’s Lane, Co. Dublin under the auspices of South Dublin Co. Council. The results of the two year study to monitor the performance of the reed willow bed facility at Lynches Lane, Co. Dublin, Ireland, will be presented. The zero discharge achieved over the 24 month period will be reviewed. The application of this system to the Irish situation will be discussed. The Danish experience with the production of their Willow guidelines and the need for no monitoring will be compared with the position Ireland now finds itself in as a result of the recent EU judgment

A Review of Zero Discharge Wastewater Treatment Systems Using Reed Willow Bed Combinations in Ireland

Sean O'Hogain et al. — Thu, 19 Apr 2012 01:26:03 PDT

The concept of a reed willow bed combination has the potential to achieve a zero discharge wastewater treatment system. This paper will present results from a two year study to monitor the performance of a reed willow bed facility at Lynches Lane, Co. Dublin, Ireland. Outline design specifications for the facility will be presented. Monitoring results for a two year period including influent and effluent parameters, rainfall, potential evapotranspiration, and soil classification will be presented and discussed. During the two year monitoring period the system achieved a zero discharge. This paper will discuss the potential widespread application of similar systems in Ireland. This is in the context of a recent EU judgment which declared that Ireland has failed to fulfill its obligations regarding domestic wastewaters disposed of through individual waste water treatment systems. The development of an appropriate zero discharge wastewater facility has the potential to address this source of environmental pollution in Ireland. This paper will discuss the sizing and operation of such systems specific to the climate and soil conditions based on current knowledge and experience. Areas for further studies will be discussed.

Pilot Rainwater Harvesting Study Ireland

Liam McCarton et al. — Wed, 18 Apr 2012 07:23:32 PDT

There are no National Water Quality Standards for Rainwater Harvesting supply in Ireland. The Development Technology Centre (DTC) at the Dublin Institute of Technology was commissioned by the National Rural Water Monitoring Committee in 2005 to assess the feasibility of using rainwater harvesting to supplement treated mains water for non-potable uses. The project involved the design, installation, commissioning and monitoring of rainwater harvesting facilities for rural domestic and agricultural water supply. This paper will present the results from the domestic pilot rwh project. A dual water supply system was designed and installed to use rainwater collected from the roof surface to supplement mains water supply for toilet flushing and out door uses. A series of flow meters and a data logger system were installed to monitor micro component household water usage. Over the 19 month monitoring period, rainwater harvesting resulted in a saving of 20% of the total mains water supplied to the house. Harvested rainwater was tested monthly for physico-chemical and microbiological parameters. All samples complied with EU bathing Water Regulations. Compliance with the more stringent Drinking Water Regulations was achieved for ten of the nineteen sampling dates. Laboratory experiments were conducted using a variety of water related bacteria to determine time required to reduce a bacterial population by 90% at a given temperature. The laboratory experiments showed that hot water systems maintained at adequately high temperatures (60 ⁰C) for 5 minutes effectively reduced the bacterial load from E.coli, Enterococcus faecalis, Pseudomonas sp and Salmonella to zero.

Determination of Characteristic Bridge DAF using Dynamic Finite Element Analysis of Critical Static Loading Scenarios

Colin Caprani et al. — Fri, 21 Oct 2011 06:13:03 PDT

The development of accurate codes for the design of bridges and the evaluation of existing structures requires adequate assessment of site-specific heavy traffic loading and also the dynamic interaction that may occur as this traffic traverses the structure. Shortcomings in current design codes occur due to the relatively independent manner in which critical static loading values and the corresponding allowance for dynamic amplification factor (DAF) are obtained. It is important that an approach is adopted that allows for the reduced probability of both high static loading and high dynamic amplification occurring simultaneously. Consideration of only relevant critical loading events will allow for efficient and accurate determination of independent values for characteristic (lifetime-maximum) static and total load effects. This paper proposes a method whereby initially the critical static loading scenarios for a chosen bridge are determined, from Monte Carlo simulation using weight-in-motion (WIM) data from a typical European route. The development of a database of 3-dimensional finite element bridge and truck models allows for the analysis of these various different combinations of vehicular loading patterns. Thus the bridge specific critical loading scenarios are modelled and analysed individually to obtain the critical total (dynamic + static) load effect. It will then be possible to obtain a correlation between critical static load effect and corresponding total load effect/DAF and to extrapolate a characteristic DAF. This approach can lead to significant savings in structural design/assessment where site-specific maximum design load effects are determined from measured traffic data and experimental bridge-truck dynamic interaction.

Estimating Risk of Failure of Engineering Structures using Predictive Likelihood

Colin Caprani et al. — Fri, 21 Oct 2011 06:13:02 PDT

It has been common engineering practice to define characteristic values for loading and capacity of structures in order to assess the structural capacity of existing structures. This approach, yet practical and intuitive, lead to the comparison of deterministic values (characteristic values) that had to represent all the variability of the problem and is considered to be conservative, as usually loading is overestimated and capacity underestimated, yielding to calculations with high safety margins for the extreme events. Probabilistics methods have tried to overcom e this limitation by computing the overall probability of failure (Pf) for the lifetime of the structure, taking into account the real probabilistic distribution of both loading and resistance. In this paper, Predictive Likelihood (PL) is presented as a powerful method to determine the lifetime distribution for loading and resistance. From these lifetime distributions the probability of failure is computed. An example of the application of the proposed method is finally presented. The result obtained using PL is then compared with the numerical approximation for the exact lifetime probability of failure.

Bridge Dynamics and Loading

Colin Caprani et al. — Fri, 21 Oct 2011 06:12:59 PDT

Recent UCD research on dynamic bridge-truck interaction and bridge traffic loading in general is reported. The accuracy of bridge traffic load assessment has been significantly improved by identifying the differences in the sources of traffic loading on short- to medium-span bridges and treating them separately. It is shown that results can be significantly improved by treating 1-,2-,3- and 4-truck loading events separately. Gaps between trucks are also identified as a critical issue that strongly influences the frequency of key3-and 4-truck events. Trends in the dynamics of traffic loading are identified using simple force models on simply supported beams. It is shown that an accurate assessment of the influence of dynamics requires a probabilistic approach. This is illustrated through an assessment of the dynamic factor for a bridge in Slovenia.

Critical Loading Events for the Assessment of Medium Span Bridges

Colin Caprani et al. — Fri, 21 Oct 2011 06:12:58 PDT

This paper describes the simulation of free-flowing traffic across bridges to predict the characteristic values for bridge load effects such as bending moment and shear force. The results of these simulations are then used to demonstrate that, in predicting the characteristic extreme load effects to which a bridge may be subjected, it is not sufficient to solely model one-or two-truck presence events. It is shown that loading events involving three or more trucks may need be included in the model for short to medium spans. The critical loading events for a particular load effect are strongly dependent on the span and the shape of the influence line.

Site-specific Probabilistic Load Modelling for Bridge Reliability Analysis

Colin Caprani et al. — Fri, 21 Oct 2011 06:12:56 PDT

Reliability assessment of a short span beam-slab reinforced concrete bridge in Vienna is proposed using site-specific traffic data recorded using the Slovenian Weigh in Motion (SiWIM) system. An initial evaluation of the bridge using a determinintic approach shows that the critical limit state is bending. This paper describes the statistical analysis of the SiWIM data and the traffic flow simulations performed to predict the characteristic extreme load effects to which the bridge may be subjected during its remaining lifetime. These values are compared to the magnitude obtained from a deterministic approach. The influence lines used in the simulations are the real structrual response obtained from the SiWim instrumentation and the theoretical influence line for bending moment at mid-span. It is argued that reliability assessment of exising structures using actual traffic loading data is more realistic than the use of deterministic loading models.

Study of Same-lane and Inter-lane GVW Correlation

Colin Caprani et al. — Fri, 21 Oct 2011 06:12:54 PDT

Extensive work has been done over the last two decades on the simulation of traffic loading on bridges. The methodology used is to generate a number of years of simulated traffic and to use extreme value statistics to predict more accurately the characteristic loading for a given bridge. The parameters and probability distributions used in the Monte Carlo simulation must be based on observed sample traffic data. Some previous studies have made unsubstantiated assumptions regarding correlation between the Gross Vehicle Weights (GVW) of trucks in the same lane, or between trucks in adjacent, same direction lanes. For this paper, an extensive database of Dutch Weigh-in-Motion data is analysed. Data are collected from two same-direction lanes and are time-stamped to the nearest 0.01 seconds. The statistical characteristics of this set of data are presentd, and various techniques are used to establish the nature and extend of GVW correlation.

Finding the Distribution of Bridge Lifetime Load Effect by Predictive Likelihood

Colin C. Caprani et al. — Fri, 21 Oct 2011 06:12:53 PDT

To assess the safety of an existing bridge, the loads to which it may be subject in its lifetime are required. Statistical analysis is used to extrapolate a sample of load effect values from the simulation period to the required design period. Complex statistical methods are often used and the end result is usually a single value of characteristic load effect. Such a deterministic result is at odds with the underlying stochastic nature of the problem. In this paper, predictive likelihood is shown to be a method by which the distribution of the lifetime extreme load effect may be determined. A basic application to the prediction of lifetime Gross vehicle Weight (GVW) is given. Results are also presented for some cases of bridge loading, compared to a return period approach and important differences are identified. The implications for the assessment of existing bridges are discussed.