Pedestrian Loading Research Articles

Experimental and Numerical Study on Dynamics of Two Footbridges with Different Shapes of Girders

The paper presents the experimental and numerical results of the dynamic system identification and verification of the behavior of two footbridges in Poland. The experimental part of the study involved vibration testing under different scenarios of human-induced load, impulse load, and excitations induced by vibration exciter. Based on the results obtained, the identification of dynamic parameters of the footbridges was performed using the peak-picking method. With the impulse load applied to both structures, determination of their natural vibration frequencies was possible. Then, based on the design drawings, detailed finite element method (FEM) models were developed, and the numerical analyses were carried out. The comparison between experimental and numerical results obtained from the modal analysis showed a good agreement. The results also indicated that both structures under investigation have the first natural bending frequency of the deck in the range of human-induced excitation. Therefore, the risk of excessive structural vibrations caused by pedestrian loading was then analysed for both structures. The vibration comfort criteria for both footbridges were checked according to Sétra guidelines. In the case of the first footbridge, the results showed that the comfort criteria are fulfilled, regardless of the type of load. For the second footbridge, it was emphasized that the structure meets the assumptions of the guidelines for vibration severability in normal use; nevertheless, it is susceptible to excitations induced by synchronized users, even in the case of a small group of pedestrians.

Pedestrian bridges and load testing

Pedestrian bridges and load testing

Vibration serviceability of a GFRP railway crossing due to pedestrians and train excitation

Glass Fibre-Reinforced Polymers (GFRPs) are a popular option for pedestrian bridges over railway lines as they cause little disruption for installation or maintenance. However, as they are typically lighter and less stiff than traditional materials there is concern about their dynamic response due to human induced actions and train buffeting. Due to a lack of experimental information, further data is needed if such bridges are to be used on future lines, especially with higher speed limits. This paper presents an experimental investigation of the response of a 14.5 m GFRP truss bridge due to pedestrian loading and train induced vibrations. Vibration modes of interest were identified from impact hammer tests. The vibration responses to a range of human loading scenarios, as well as multiple train passes, were measured. The vibration levels remained low under all conditions, demonstrating that this particular type of GFRP bridge is suitable for railway crossings and that further optimisations may be available to designers while meeting vibration serviceability limits. However, consideration of the loadings suggests GFRP bridges may be more susceptible to higher pedestrian harmonics than traditional structures, and that vibrations from train buffeting are likely to be a design consideration for future bridges over high speed lines.

Testing Walking-Induced Vibration of Floors Using Smartphones Recordings

Smartphone technology is rapidly evolving, adding sensors of growing accuracy and precision. Structural engineers are among customers who indirectly benefit from such technological advances. This paper tests whether accelerometers installed in new generations of smartphones can reach the accuracy of professional accelerometers created for vibration monitoring of civil engineering structures, and how they can be useful. The paper describes an experimental study designed to measure walking-induced vibrations of a slender prefabricated prestressed concrete slab. Both traditional, high-accuracy, accelerometers and those integrated into commercial smartphones were used for experimental data collection. Direct comparison of the recordings yielded two key findings: the accuracy of smartphone accelerometers largely depends on the specific smartphone model, and nevertheless is satisfactory for preliminary modal testing at the very least. Furthermore, the smartphone measured accelerations of the lower back were used successfully to indirectly measure pedestrian walking loads.

Experimental investigation on the potentials of Sisal Fibres as Reinforcements for Drainage Concrete Cover Plates

With the development of infrastructures in Rwanda, the roads construction has been one of busiest area, and as the country counts thousands hills the design and construction of drainage systems required a great attention. Most of road drainage channels are covered with concrete plates that are reinforced with ordinary steel bars, while others are not covered due to the high cost of reinforced concrete plates. As the majority of these plates are only subjected to light pedestrian loads, they should be reinforced accordingly. This study was intended to check the potentials of sisal fibres from Agave Sisalana’ cactus plant which has shown good results in flexural members, as plates reinforcements. At first the quality of ordinary concrete components was checked. Then some of sisal fibres were prepared, manufactured into ropes of 10 mm diameter and then used as replacements of main steel bars in concrete plates before their tensile capacity was checked. Other pieces of sisal fibres of 5 cm length were mixed in concrete mass with different percentages of 0.5%, 1% and 1.5% of concrete volume. Test results showed that the compressive, tensile and flexural strengths for concrete with 1% of sisal fibres were more adequate for M30 concrete and therefore able of sustaining the real loads applied to the drainage concrete cover plates. As the performance of natural sisal fibres depends on fibres treatment methods, length, and type of required concrete, further studies on the use of sisal fibres should consider those factors.
 Keywords: Agave sisalana, drainage channel, Reinforced Concrete, Sisal Fibres, Sisal ropes.

Structural health monitoring and seismic response assessment of bridge structures using target-tracking digital image correlation

Our nation’s infrastructure is aging and deteriorating which increases the need for condition assessment and structural health monitoring. For this purpose, there is a growing interest in using non-contact monitoring methods because of the challenges associated with deploying and installing conventional instrumentation. Target-tracking digital image correlation (DIC) is among these methods and is the focus of this paper. Several research activities have been conducted at the University of Nevada, Reno in the field of dynamic monitoring using DIC and presented here. The first part of the paper is concerned with a large-scale laboratory application where target-tracking DIC was utilized to monitor the response of a bridge structure tested under bidirectional earthquake shaking. The 3D dynamic response of the bridge, along with modal properties, i.e. natural frequency, damping ratio, and mode shapes, were measured or determined using both DIC and conventional instrumentation then compared for validation purposes. The second part of the paper presents results from field monitoring of an actual footbridge under pedestrian loading to determine the vibration frequencies of the bridge, and again compare it against results from conventional accelerometers for validation. From both applications, the DIC is demonstrated to successfully capture (1) peak and residual bridge deck rotation and deformation under different earthquake intensity levels and (2) modal properties for system identification. Practical DIC sampling rates were used to accurately monitor and capture the dynamic response of bridges, which shows a high potential for using DIC for larger structural health monitoring applications and future reconnaissance works.

Estimation of modular green roof systems installation using the method of chronometry measurements

Due to the experimental studies using the method of timing measurements, the temporal values of technological operations for the installation of modular landscaping systems were calculated and technological works that have a great influence on the total device construction time were determined. A comparative analysis of the complexity of the device layers of the used coating showed that the most time-consuming is the process of laying paving slabs - 45 people-hours / 100 sq.m. (80% of the total complexity of the device layers of the used coating). Technological processes and operations associated with the installation of the pavement with the use of paving slabs under pedestrian load are more labor-intensive compared to the installation of landscaping systems. The average value of the complexity of the device operating cover for pedestrian load is 56.7 people-hours / 100 sq.m., while the average value of the complexity of the device of the coating with peeling systems is 15.6 people-hours / 100 sq.m., which is 28% lower than the complexity of the device operating cover for pedestrian loading.

Further steps towards the tuning of inertial controllers for broadband‐frequency‐varying structures

There is a large number of slender structures which are prone to vibrate due to pedestrian loads. The well-known Tuned Mass Damper (TMD) is increasingly used in practice, but this device may detune under several circumstances drastically reducing its expected performance. A Semi-active TMD (STMD) provides more robustness under structure uncertainties than the passive one and may be recommended for use when several vibration modes are in the excitation range and/or when the mode to cancel has uncertainty or varies over time. The tuning of the semi-active device for these cases cannot be the same as the passive one. This paper presents a methodology for the tuning of an STMD under broad frequency-band uncertainties using an ON/OFF phase control law. This control law is experimentally implemented considering interesting practical aspects, such as the estimation of the inertial mass velocity from the measured acceleration, or a low-pass filter to avoid unnecessary control actions, among others. An optimization process using a proposed performance index is carried out. Thus, it has been demonstrated that the optimal STMD is achieved for much lower damping and higher tuned frequency than the passive one. Finally, the proposed methodology is validated with experimental results.

Dynamic Analysis of Suspension Footbridges Using an Actual Pedestrian Load Model Compared with EUR23984 EN Requirements

The suspension footbridges are very flexible due to their geometrical structure; hence they may face severe vibration problems induced mainly by natural forces and pedestrians crossing. By exceeding a certain limit, these vibrations can disturb the serviceability of the bridge as well as health and safety of the structure and pedestrians. Therefore, standard design guidelines are sets of recommendations to control the vibrations by applying restrictive design criteria. Because of the complexity of the exact simulation of the human-induced loads, these guidelines provide simplified methods to cover the frequency ranges of the human motion types in order to estimate the response of the structure without modeling the actual motion. As current paper, the simplified loading method proposed by EUR23984 EN code‑as the main footbridge design standard was investigated. Its compliance with pedestrian’s synchronization phenomenon was evaluated using the analysis results of a discontinuous type loading model proposed by authors. It was shown that the response of the footbridge strictly depends on the type and the speed of the pedestrian motion applied to the bridge, which is not included in the design parameters of the code. In this research work, a series of analysis is conducted on a suspension footbridge as a case study under both actual human loads and the simplified loads suggested by the code and the results were compared. It was found out that in the same crowd loading, the actual human loading creates greater vertical accelerations compare to EUR 23984 EN method results.

BRIDGE RE-DESIGN CLASS A COMPOSITE GIRDER (GIRDER BRIDGE CASE STUDY OF COMPOSITE CLASS C+) RANTAU BAKULA BANJAR DISTRICT

In Rantau Bakula village are its main bridge girder composite construction. Due to the condition of the existing bridge is felt not designed for vehicles with a large payload then re-design bridge girder composite with spans of 25 m and 9 m wide bridge.In this planning will be carried out load analyzes include: self weight, additional dead load (weight of asphalt and rainwater), load lane "D", pedestrian live load, brake force, load the truck "T", the wind load and earthquake load. Loading method refers to the imposition Standards For RSNI Bridge T-02-2005 whereas the method of structural design of composite bridges refers RSNI T-03-2005 Steel Structural Design For Bridge and SNI 03-1729-2002 on Procedures Design Steel Structures. From the planning to the pavement reinforcement obtained using principal reinforcement D 13-150 mm with shear D 13-90 mm. The main girder profiles used WF 900 x 300 x 16 x 32 and diaphragm WF 400 x 200 x 8 x 13 shear connector used stud with a size of 12 x 190 mm. The connection between girders using screws with a diameter of 20 mm. Abutment has a height of 2.75 m and a length of 10 m. Used caisson foundation amounted to 2 pieces with a length of 2 meters and a diameter of 3.5 m. Keywords: Rantau Bakula, bridge, girders, composite abutments, caisson.

Prediction of resonantly forced vibrations for suspended footbridges

The aim of the present paper is to investigate the performance of suspended footbridges under pedestrian loads. Indeed, several Authors have underlined the possible activation of large amplitude oscillations into suspended footbridges due to the nonlinear behavior of the hangers. In fact, the last ones act as linear elastic springs in tension and do not react in compression. Consequently, if the whole suspended footbridge or parts of it undergo large amplitude oscillations, the initial hangers’ pretension stress may become zero and the slackening may start. In these cases, the stiffness of the footbridge deck decreases drastically, and a complex dynamic response may occur. Hence, the footbridge may show unexpected vertical and torsional oscillations that the “classical” models cannot predict; these models, in fact, assume a bilateral behavior for the suspended system and, consequently, no variations of the global stiffness during the motion. Here, the response of suspended footbridges is evaluated by using a continuous model obtained by adopting the nonlinear equivalent regularization technique proposed for long span suspended bridges. The dynamic analysis, performed by means of a perturbation method, shows the possibility of the coexistence of multiple solutions, some of which are characterized by high amplitudes and by the activation of the afore-described slackening phenomenon. The response is evaluated for several values of loading, mechanical and geometrical parameters, with the main aim of highlighting the characteristics and the stability of the investigated oscillations and obtaining information and/or design indications to prevent such phenomena.Communicated by Dumitru Caruntu.

Study on nonlinear parametric vibration of footbridge considering time-lag effect

Under the action of pedestrian dynamic load, a pedestrian bridge with large span and light flexibility will show the nonlinear characteristics of the structure, and there is a time lag phenomenon in the feedback of the pedestrian’s force on the pedestrian bridge. Therefore, based on the derivation of the nonlinear dynamic model of the parametric vibration of pedestrian bridge, the time lag effect is introduced. Taking the Millennium Bridge of London as an example, the influence of time-lag on parametric vibration of pedestrian bridge is analyzed. By using Galerkin method and multi-scale perturbation method, theoretical and numerical analysis of large vibration induced by parametric vibration and forced vibration of pedestrian bridge is carried out. The amplitude frequency curve of nonlinear parametric vibration with time-lag effect is obtained, and it is concluded that the time-lag of nonlinear parametric vibration in Millennium Bridge has no effect on the amplitude of the structure, but only affects the peak arrival time and the time of stable amplitude. And the conclusion is proved by the numerical analysis.

Investigation of vibration data-based human load monitoring system

Structural design of flexible footbridges requires a thorough understanding of pedestrian-induced vibration such that their dynamic behavior is accurately predicted. Human-induced vibration creates complicated ground reaction forces that contribute to human–structure interaction in the footbridges. It, therefore, becomes a significant challenge to the bridge designers to accurately estimate the moving pedestrian load on the footbridges during the design phase. This article examines the issues of human–structure interaction in slender pedestrian bridges and aims to analyze the walking pattern of the pedestrian from human-induced vibration data of the bridge. A wavelet-based time–frequency decomposition technique is adopted to extract the walking pattern of the pedestrian followed by time-series analysis of the walking pattern to develop a statistical model of pedestrian-induced vibration. Full-scale testing is conducted on a footbridge to validate the proposed technique under a wide range of pedestrian excitation. An experimental study is conducted to demonstrate the proposed method using the pedestrian’s walking on a force plate monitored by video cameras and vibration sensors. Identified walking patterns are then compared with the actual walking patterns measured by motion sensors attached to the test subject.

Analysis on vibration control of a large-span pedestrian suspension bridge based on a multiple tuned mass damper system

Tuned mass damper is one of the commonly used passive control devices. It is the earliest used device in civil engineering control of vibration control of high-rise buildings and towering structures. For large-span pedestrian bridges, the pedestrian load spectrum covers many modalities of pedestrian bridges. It is difficult to achieve the expected results with a single tuned mass damper device. In order to obtain efficient damping, the multiple modes of a multiple tuned mass damper which may resonate under excitation are controlled. This chapter adopts the pedestrian suspension bridge over Dongtan River as the subject to arrange a multiple tuned mass damper system in the finite element model of the pedestrian suspension bridge, analyze the effectiveness of the multiple tuned mass damper system on the control of human-induced vibration of a large-span pedestrian suspension bridge, and discuss the vibration reduction effect of the multiple tuned mass damper system on the response to human-induced vibration of the pedestrian suspension bridge. The analysis shows that a multiple tuned mass damper system has a significant effect on controlling human-induced vibration of the pedestrian suspension bridge.

Vibration serviceability assessment of GFRP pedestrian bridges

Over the past few decades, fibre-reinforced polymer (FRP) materials in general and glass-fibre-reinforced polymer (GFRP) in particular have become popular and competitive solutions in the construction of bridge objects. Because of their properties – such as high strength to weight ratios, ease of structure assembly, non-conductivity and chemical resistance – significant applications of the composite materials have been realised in the construction of footbridges in particular. In this paper, a numerical evaluation of the serviceability behaviour of two examples of composite material footbridges is presented. For the purpose of the study, it was assumed that the footbridges were made of the same composite material but they differ from each other with regard to structural geometry. The first stage of the study was the numerical estimation of the modal characteristics of the footbridges, i.e. their mode shapes and natural frequencies. The risk of the resonance phenomenon caused by pedestrian loading was then considered for both structures. In the next step of the calculations, the authors assessed the dynamic response of the footbridges to typical traffic loads; these types of load are transmitted to the structure through the ground and foundations. For numerical analysis, finite element (FE) models of the footbridges were prepared in the ABAQUS/Standard software program. The calculations included the representative time histories of the passage of a heavy goods vehicle and trains. Finally, the vibration comfort criteria for both footbridges were checked. The obtained results show that the comfort criteria are fulfilled.

A completely non-contact recognition system for bridge unit influence line using portable cameras and computer vision

Currently most of the vision-based structural identification research focus either on structural input (vehicle location) estimation or on structural output (structural displacement and strain responses) estimation. The structural condition assessment at global level just with the vision-based structural output cannot give a normalized response irrespective of the type and/or load configurations of the vehicles. Combining the vision-based structural input and the structural output from non-contact sensors overcomes the disadvantage given above, while reducing cost, time, labor force including cable wiring work. In conventional traffic monitoring, sometimes traffic closure is essential for bridge structures, which may cause other severe problems such as traffic jams and accidents. In this study, a completely non-contact structural identification system is proposed, and the system mainly targets the identification of bridge unit influence line (UIL) under operational traffic. Both the structural input (vehicle location information) and output (displacement responses) are obtained by only using cameras and computer vision techniques. Multiple cameras are synchronized by audio signal pattern recognition. The proposed system is verified with a laboratory experiment on a scaled bridge model under a small moving truck load and a field application on a footbridge on campus under a moving golf cart load. The UILs are successfully identified in both bridge cases. The pedestrian loads are also estimated with the extracted UIL and the predicted weights of pedestrians are observed to be in acceptable ranges.

RELATION BETWEEN STATIONARY AND MOVING PEDESTRIAN LOAD MODELS

The dynamic analysis of footbridges became common in recent years, but the approach to modelling pedestrian induced load is still inconsistent. This paper compares two different ways of modelling single pedestrian load. The response of the structure to stationary pulsating force is compared to the results given by the same force moving along simply supported beam. 300 randomly generated beams were used in this parametric study to describe the relation among these two approaches and parameters of the structure. The proposed formula was successfully applied to get more realistic estimation of response of the structure to a single walking pedestrian using stationary pulsating force.

Review of Pedestrian Load Models for Vibration Serviceability Assessment of Floor Structures

Innovative design and technological advancements in the construction industry have resulted in an increased use of large, slender and lightweight floors in contemporary office buildings. Compounded by an ever-increasing use of open-plan layouts with few internal partitions and thus lower damping, floor vibration is becoming a governing limit state in the modern structural design originating from dynamic footfall excitations. This could cause annoyance and discomfort to building occupants as well as knock-on management and financial consequences for facility owners. This article presents a comprehensive review pertinent to walking-induced dynamic loading of low-frequency floor structures. It is intended to introduce and explain key walking parameters in the field as well as summarise the development of previous walking models and methods for vibration serviceability assessment. Although a number of walking models and design procedures have been proposed, the literature survey highlights that further work is required in the following areas; (1) the development of a probabilistic multi-person loading model which accounts for inter- and intra-subject variabilities, (2) the identification of walking paths (routes accounting for the effect of occupancy patterns on office floors) coupled with spatial distribution of pedestrians and (3) the production of a statistical spatial response approach for vibration serviceability assessment. A stochastic approach, capable of taking into account uncertainties in loading model and vibration responses, appears to be a more reliable way forward compared to the deterministic approaches of the past and there is a clear need for further research in this area.

Design and optimisation of an underfloor energy harvesting system

Piezoelectric stack energy harvesters have the advantage of generating electrical power for small amounts of deflection. In an underfloor energy harvesting application, this is advantageous as the device does not disrupt the gait of pedestrians overhead. Low frequency, stochastic loading patterns are typical of underfloor applications, where the precise gait, weight and number of pedestrians are unpredictable. Energy harvesters targeting this type of directly applied load are faced with the challenge of providing sufficient force for power generation and determining appropriate matching of the piezoelectric stack to the circuit being powered, to achieve the highest possible energy conversion efficiency. The latter is particularly challenging in the case of stochastic input, due to the piezoelectric stack’s dependence on frequency. To address these challenges, a force amplification frame is used in conjunction with a piezoelectric stack to provide an increase of up to 10 times of the applied load to the stack. A method of modelling the energy harvester is presented to optimise the device to suit a range of typical inputs, including walking, jogging and multiple pedestrian loading conditions. The methods used are capable of incorporating measured data from existing support platforms and the behaviour of interfacing power management circuitry into the optimisation loop, providing an accurate means of predicting the response of the energy harvesting system under typical operating conditions. The model is experimentally validated, and the results used to demonstrate a potential power increase of a factor of 21 when compared to an off-the-shelf piezoelectric stack.

Study on vertical vibration control of long-span steel footbridge with tuned mass dampers under pedestrian excitation

This paper aims to study crowd-induced vibration control of long-span steel footbridges with different dynamic characteristics by combining methods of site measurement and numerical simulation. Four kinds of footbridge models with sensitive vertical natural frequencies of easily generating human-bridge resonance under pedestrian loading are designed based on an actual steel footbridge. The numerical models are firstly validated by comparative investigation between the site measurement and the simulation. Detailed study on dynamic responses of the four footbridges with and without controlling systems of tuned mass damper (TMD) and multiple tuned mass damper (MTMD) is then conducted under 13 cases of crowd random excitations, rhythmic running and jumping excitations. Results show that the numerical simulation agrees well with the site measurement data. TMD system is found to be highly efficient in reducing vibration responses only when the excitation frequency is basically consistent with the structural natural frequency, which obviously limits the application of TMD system in footbridges as wider excitation frequency bandwidth is caused by human activities. MTMD system are demonstrated to be with higher vibration absorption robustness appearing predominant and stable capacity of reducing structural vibrations under all the crowd random and rhythmic excitations for the four footbridges.