Vertical Stiffness Research Articles

Shaking table test on seismic performance of integrated station-bridge high-speed railway station

The structure of integrated station-bridge is commonly used in the construction of high-speed railway station, which mainly consists of the frame part and the grid part. The complicated structure is characterized by the discontinuous vertical stiffness and the large longitudinal span, which results in an undefined mechanism of structural dynamic catastrophe. In this paper, the shaking table test was carried out with the model scale ratio of 1/25 to study the seismic performance, including the failure mode, acceleration, displacement and internal force responses, etc. The results show that the buckling of the frame occurs under the PGA of 0.82 g, which mainly concentrates on the third floor. The beam end of the top joint buckles obviously under the PGA of 1.27 g. The members of grid begin to yield under the PGA of 0.40 g, in which the order of yield member was web and chord in the truss. Based on the results of experiments, a seismic performance evaluation method of the composite structure is proposed for the damage of the grid frame and frame under different seismic intensities.

Influence of metro track parameters on vibration characteristics of vibration damping track

In view of the abnormal wear of the vibration damping track with small radius curve on the subway, the vibration and noise problems associated with it have been widely concerned by society. The dynamic model of vehicle-track system including elastic damping track is established by using simulation software. The influence of structural parameters of steel spring floating slab track (SSFST) with small radius curve on the mode and vibration frequency, as well as the resonance characteristics of elastic track structure are analyzed. The results show the following: (1) Increasing the length of floating slab can effectively reduce natural frequency, while the range of frequency variation caused by the thickness of floating slab is relatively small. The length and thickness of floating slab can be properly adjusted to avoid the track resonance. (2) It is more integrated for the rail and floating slab through increasing the vertical stiffness of fastener, which increases the vibration frequency of the track structure. There is little effect on the vibration characteristics of SSFST for changing the installation spacing of steel springs. (3) It is more obvious for resonance to occur between the inner rail and floating slab at 116 Hz, 130 Hz and 161 Hz, and the track vibration mode shows multi-step reverse vibration on both sides and overall vertical bending vibration. (4) Due to the unbalance load caused by curve superelevation, the inner wheel weight plays the restraining role, which makes the inner rail and floating slab have various forms of bending deformation in a certain frequency range, increasing the complexity of the bending deformation of the track structure.

Vertical response of unbonded fiber reinforced elastomeric isolators (U-FREIs) under bidirectional shear loading

Fiber Reinforced Elastomeric Isolators (FREIs) were generally studied in unbonded configuration. Due to combined axial and shear loads, the contact area between the bearing and horizontal supports reduces with the horizontal displacement. As a result, both the vertical and the horizontal stiffnesses decrease with the horizontal deformation while also the vertical deformation increases. This paper presents the results of a large set of full-scale 3D Finite Element Analyses on unbonded fiber reinforced bearings with different geometries, subjected to combined axial and multi-directional shear loads. The main vertical response parameters were studied, namely the vertical displacement, the vertical stiffness, and the effective compressive modulus, thus highlighting the influence of both geometry and horizontal loading direction on the vertical response of the FREIs. Conclusion of this study demonstrate to what extent the combined influence of geometric properties and loading conditions affects the vertical response of elastomeric bearings with flexible reinforcements.

Probability Distribution Characteristics of Horizontal and Vertical Mechanical Properties of Rubber Bearings.

Rubber bearings are widely used to protect civil structures from destructive earthquakes. The mechanical properties of the bearings are the key technical parameters that determine the seismic isolation performance of isolated structures. To estimate the probability distribution of the mechanical properties related to rubber bearings (including horizontal stiffness, vertical stiffness, post-yield stiffness and yield force) under seismic events. Typical natural rubber bearings (NRBs) and lead-core rubber bearings (LRBs) were designed and fabricated, and the bearings were subjected to repeated load tests using a compression-shear testing machine. The test results of the horizontal and vertical mechanical properties of the bearings in the tests were basically consistent with the design values, and the rubber bearings showed stable mechanical behavior under repeated cyclic loading. The statistical analysis of the test results revealed that the relevant mechanical properties of the NRB and LRB specimens followed a lognormal or general extreme distribution with coefficients of variation mainly ranging from 0.86% to 5.6%. The dispersion of the yield force of LRB was the largest in the repeated tests of many mechanical parameters of typical rubber bearings.

Consolidation settlement of vertically loaded pile groups in multilayered poroelastic soils

Pile groups are commonly used as the foundations of many structures including those used in transportation infrastructures. Consolidation settlement of a pile foundation is an important design parameter. A theoretical model is developed in this study to estimate the consolidation settlement and axial load transfer of vertically loaded pile groups in multilayered poroelastic soils. The multilayered saturated soil is modeled according to Biot’s poroelasticity theory. In order to determine quasi-static response of pile groups, the interaction problem is first formulated in the Laplace transform domain. Vertical displacement compatibility is enforced at the pile-soil interface to simulate the pile group-soil interaction. Axial deformation of each pile is represented by an exponential series with undetermined coefficients, which are obtained from a variational approach. Vertical displacement influence functions due to a buried uniform vertical load applied to the layered soil are required in the formulation. The application of an exact stiffness matrix method yields the required influence functions. Time-domain solutions are obtained by employing a numerical Laplace inversion method. Numerical results for time-dependent vertical stiffness and consolidation settlement are presented for different pile group configurations, layer profiles, pile elastic moduli and pile lengths.

Development of a long-period vertical base isolation device with variable stiffness for steel frame structures

The current isolation technology is mainly developed for seismic response control of structures in horizontal direction. Seismic records and shaking table test results show that there is a strong need to mitigate the vertical responses of structures. This paper proposes a three-dimensional (3D) isolation device that consists of a traditional horizontal bearing and a newly developed long-period vertical isolation device with variable stiffness (LVIVS). The LVIVS includes three layers of springs and two of them are prestressed. With the aid of displacement constraint components, the non-prestressed springs work independently or in series with the prestressed springs at different loading stages to realize variable stiffness characteristic. As designed, the LVIVS has large vertical stiffness in the normal stage to restrain the displacement under live loads and ground motions with small amplitudes, small vertical stiffness in the isolation stage to prolong the vertical period of the base isolation system, and large vertical stiffness in the limit stage to restrain large vertical displacement at extreme events. The prestress of the springs leads to a self-centering feature of the device. Also, the variable stiffness characteristic shortens the deformation demand of the device under self-weight which enhances the stability of the device significantly and thus it is easier to achieve a long isolation period in the isolation stage. The hysteretic model for the LVIVS is derived, and sinusoidal excitation tests are conducted to verify the proposed hysteretic model of the LVIVS and its variable stiffness mechanism. The experimental results show that the variable stiffness characteristics of the LVIVS can be achieved, and the isolation period reaches 0.95 s. Finite element simulations are also conducted for a steel frame structure to verify the isolation effect of the proposed 3D isolation device.

Stiffness contributions of ballast in the context of dynamic analysis of short span railway bridges

Railway bridges are subjected to intensive dynamic loading. In structural calculations, the resulting response is estimated by dynamic calculations. As the basis of these calculations, the system's natural frequencies are to be numerically determined. Various studies have shown that a discrepancy between these measured natural frequencies and the numerical determination often occurs for short-frame bridges. In common practice, the ballast is assumed to be non-contributing to the global structural stiffness. In some cases, rheological models are developed to consider possible ballast stiffnesses based on small-scale model tests. The resulting spring-damper models are based on empirical values and are not directly related to the material behaviour of ballast.This paper discusses the ballast stiffness at the material level using relationships known from soil dynamics. The research shows that the material properties of the ballast can be determined in terms of stress and shear strain dependence. An equivalent ballast stiffness can be determined and considered in dynamic calculations for a known stress state and corresponding superstructure accelerations. The paper presents an approach for determining vertical and horizontal ballast stiffness according to shear strains and superstructure accelerations.This developed approach is validated by experimental tests using a small-scale bending beam and accompanying numerical calculations.Furthermore, a parameter study shows that the stiffness of the ballast does not contribute significantly to the global bending stiffness. Thus, the first bending natural frequency is hardly influenced by the ballast track.

An elastic model for the prediction of the lateral response of Cross-Laminated Timber shear walls with openings

This paper presents an analytical model for the prediction of the lateral response of Cross-Laminated Timber shear walls with openings. The model specifically deals with the rocking mechanism of monolithic shear walls with openings, includes both cases of door and window openings, and considers both cases of kinematic behaviour with one and two centres of rotations. Mathematical expressions for the prediction of the wall segment rotations, the wall segment vertical uplift and the rocking stiffness of the system are derived from the analytical model and presented in the study. The analytical model, which was validated through numerical analyses and the results of an experimental study available in the literature, was used to perform a parametric analysis, in which the lateral rocking behaviour of shear walls with different geometrical and mechanical properties and with different hold down configurations was investigated. Results of the parametric analysis showed that the rocking stiffness of monolithic shear walls with openings is strongly related to their kinematic behaviour. The mathematical expressions found in this study reveal that the kinematic behaviour of these systems mainly depends on the transversal stiffness of lintels and parapets, on the vertical stiffness of the hold downs and on the geometry of the wall segments.

Investigation on vertical stiffness reduction of thick rubber bearings under lateral displacement

Elastomeric bearings with thick rubber layers, called Thick Rubber Bearings (TRBs), can be used as three-dimensional (3D) isolators. During their design, the vertical stiffness is a critical parameter. This study focuses on exploring the parameters that influence the vertical stiffness reduction of TRBs and on developing a simplified method for its prediction. Four full-scale TRBs with various first and second shape factors (S1 and S2) were designed and subjected to axial tests under lateral displacement. Their vertical stiffness was determined. The experimental results showed that for bearings with a lower S1, the vertical stiffness under small lateral displacement increases and then decreases as the lateral displacement increases. Then, tests at the material and isolator levels were used to calibrate a finite element (FE) model of TRBs. A parametric FE study was carried out to investigate the effects of various parameters on the normalized vertical stiffness of TRBs over a wide range of lateral displacements. The study quantified the vertical stiffness reduction for different values of pressure, S1, and S2. It also evaluated code recommendations for the steel shims used in TRBs. Then, existing formulations were compared to numerical results and it was shown that they cannot accurately predict the reduction of the vertical stiffness of TRBs. Finally, an empirical formulation considering the variation in S1 and S2 of TRBs was proposed. The predicted results showed good agreement with the numerical data.

Dead Load Allocation in Triple-Cable Suspension Bridges by Adjusting the Unstrained Lengths of Hangers: A Novel Analytical Approach

Triple-cable design of suspension bridges with an ultrawide main girder can improve their mechanical properties, making it lucrative for numerous engineering scenarios. However, its realization requires assigning an appropriate share of the dead load of the main girder supported by three main cables to avoid the middle main cable overload by the main girder’s dead load since the latter would impair the mechanical behavior of the upper transverse beams in the towers and deteriorate the whole bridge’s torsional stiffness. Therefore, this study proposes an analytical approach for dead load allocation to the suspension bridge with three main cables, which adjusts the share of the main girder’s dead load supported by three main cables via changing the unstrained lengths of the hangers. The main advantage of the proposed approach is that it can consider both uniform and nonuniform allocations. The spatial model for the suspension bridge with three cable planes is first converted into a plane model. The relationship between unstrained lengths of the three hangers in the same cross section is determined via the deformation compatibility conditions and one of the following options: (1) equality of stiffness of the two side hangers in the case of a symmetrical plane model; or (2) energy conservation conditions in case of an asymmetrical one. The proposed method was applied to an example of a triple-cable suspension bridge with a main span of 2,100 m and a width of 75 m, and its analytical solutions were compared against finite-element method calculation results. An increase in the share of the main girder’s dead load supported by the two side main cables increased the torsional stiffness of the whole bridge and reduced the vertical load exerted by the middle main cable on the top transverse beam of each tower. Meanwhile, variation of the share of the main girder’s dead load supported by the side and middle main cables only slightly influenced the whole bridge’s vertical and lateral stiffness values. The aforementioned adjustment by the proposed method could be accomplished without increasing the steel consumption of the bridge cables. The results could provide references for the design, static, and dynamic response analysis of similar triple-cable ultrawide suspension bridges.

Effects of Aging and Fitness on Hopping Biomechanics.

Physical exercise promotes healthy aging and is associated with greater functionality and quality of life. Muscle strength and power are established factors in the ability to perform daily tasks and live independently. Stiffness, for mechanical reasons, is another important constituent of running performance and locomotion. This study aims to analyze the impact of age and training status on one-legged hopping biomechanics and to evaluate whether age-related power decline can be reduced with regular physical exercise. Forty-three male subjects were recruited according to their suitability for one of four groups (young athletes, senior athletes, young controls and senior controls) according to their age (young between 21 and 35, vs. older between 59 and 75) and training status (competing athletes vs. non-physically active). The impact of age and training status on one-legged hopping biomechanics were evaluated using the two-way analysis of variance (ANOVA) method. Significant differences among groups were found for hopping height (p < 0.05), ground contact time (p < 0.05), peak ground reaction force (p < 0.05) and peak power (p < 0.01). No differences among groups were found in ground-phase vertical displacement and vertical stiffness (p > 0.05). Young athletes and older non-physically active people achieved the best and worst performance, respectively. Interestingly, there were not any differences found between young non-physically active people and senior athletes, suggesting that chronic training can contribute to partly offset effects that are normally associated with aging.

Mechanical properties of coarse asphalt Mixture-Paved trackbed under High-Speed moving train loads

The long-term stability of the substructure is a critical guarantee for the safety and ride comfort of high-speed railway (HSR) operations. The asphalt mixture-paved trackbed (APT) can not only play a favorable role in preventing and draining water on the top of the subgrade but also be beneficial to the gradual change of vertical stiffness between layers. This paper determines a coarse but dense-graded asphalt mixture suitable for the APT and numerically analyzes the mechanical properties of APT under high-speed moving train loads. The results indicate that the SBS-modified asphalt mixture (SBS-25) with the optimum asphalt content (OAC) of 4.2 % is more appropriate than the crumb rubber-modified asphalt mixture (CRMA-25) for the APT. The dynamic stress in the subgrade of APT is significantly determined by the conditions of the AC layer. Meanwhile, the vibration attenuation of APT is directly related to temperature change. Compared with the traditional ballastless track, the vibration acceleration of APT with trackbed thickness of 300 mm reduces by 20.1 % at 20 ℃ while only reducing by 1.7 % at 40℃. Moreover, the greater the structural stiffness of the APT, the stronger the control on dynamic deformation of each layer in the subgrade, and the influence on the formation is weaker than that on the bottom layer of the subgrade. The findings hopefully contribute to the APT substructure design; however, further verification of real engineering still needs to be conducted by field or full-scale tests.

Ballast shear effects on the dynamic response of railway bridges

Single-track railway bridges are susceptible of experiencing high levels of vertical acceleration on the deck that may be dangerously accentuated at resonance. This is especially critical for short-to-medium span simply supported bridges. This problem can compromise the safety of the trains and increase the maintenance costs of the track. The main objective of this work is to investigate the influence of the ballasted track on the dynamic behaviour of these structures. The present contribution provides a detailed sensitivity analysis over a wide single-track bridge catalogue covering span lengths from 10 to 25 m and considering two common deck structural typologies: girder-deck and slab-deck bridges. The effect of the vertical stiffness of the neoprene bearings is also evaluated. A 2D Finite-Element track–bridge interaction model is implemented and used to analyse the effect of the track on the modal parameters, harmonic response and vertical acceleration of the bridges under train passages. Additionally, the weak coupling exerted by the track is studied for structures with an increasing number of consecutive spans. The results obtained reveal a notable influence of the mobilised ballast shear transfer mechanism on the dynamic response of the structures, especially for the shortest girder bridges. Finally, a track–bridge interaction model of an existing short girder bridge from a conventional railway line is updated and used to predict the experimental response measured under operating conditions. The adequacy of the numerical tool and influence of the ballast shear parameters on the dynamic response are shown.

On the nonlinear hunting stability of a high-speed train bogie

The hunting phenomenon is an intrinsic swaying motion appearing in railway vehicles due to the vehicle’s forward speed and the wheel–rail contact forces. Hunting motion consists of wheelset and other vehicle’s components oscillations that arise above a certain vehicle’s speed known as critical or hunting speed. These oscillations are of unstable nature and represent a safety hazard as they could lead to the vehicle’s derailment. This article analyses the stability of a bogie nonlinear model for a Spanish high-speed train when this is travelling at speeds near the hunting speed. The vehicle’s stability is studied by means of root loci methods, and the value of the critical speed is found. In addition to this, the behaviour of the vehicle is studied in both stable and unstable regions and the existence of limit cycles is discussed in this work. Finally, a sensitivity analysis of the axle load and suspension parameters is performed. The results show that the axle load, the vertical stiffness of the primary suspension and the lateral damping of the secondary suspension have a significant influence on the value of the critical speed.

Influence of dynamic stretching on ankle joint stiffness, vertical stiffness and running economy during treadmill running.

The purpose of the present study was to investigate whether and how dynamic stretching of the plantarflexors may influence running economy. A crossover design with a minimum of 48 h between experimental (dynamic stretching) and control conditions was used. Twelve recreational runners performed a step-wise incremental protocol to the limit of tolerance on a motorised instrumented treadmill. The initial speed was 2.3 m/s, followed by increments of 0.2 m/s every 3 min. Dynamic joint stiffness, vertical stiffness and running kinematics during the initial stage of the protocol were calculated. Running economy was evaluated using online gas-analysis. For each participant, the minimum number of stages completed before peak O2 uptake (V̇O2peak) common to the two testing conditions was used to calculate the gradient of a linear regression line between V̇O2 (y-axis) and speed (x-axis). The number of stages, which ranged between 4 and 8, was used to construct individual subject regression equations. Non-clinical forms of magnitude-based decision method were used to assess outcomes. The dynamic stretching protocol resulted in a possible decrease in dynamic ankle joint stiffness (−10.7%; 90% confidence limits ±16.1%), a possible decrease in vertical stiffness (−2.3%, ±4.3%), a possibly beneficial effect on running economy (−4.0%, ±8.3%), and very likely decrease in gastrocnemius medialis muscle activation (−27.1%, ±39.2%). The results indicate that dynamic stretching improves running economy, possibly via decreases in dynamic joint and vertical stiffness and muscle activation. Together, these results imply that dynamic stretching should be recommended as part of the warm-up for running training in recreational athletes examined in this study.

In-situ testing and finite element model updating of a long-span cable-stayed bridge with ballastless track

Ballastless track is widely used in high-speed railways due to its long service life, low maintenance costs, and excellent riding comfort. However, laying a ballastless track on a long-span bridge remains a challenge because of the large deflection and uneven stiffness of the long-span bridge. Limited research has been reported on the experimental behavior of the long-span railway bridge laid with the ballastless track. This study presents the in-situ testing and the finite element model updating (FEMU) of the Ganjiang Bridge, China’s first long-span ballastless railway cable-stayed bridge with a main span that reaches up to 300 m before its opening for operation. The study’s primary purposes include evaluating the mechanical properties of the ballastless railway bridge and establishing a baseline finite element model for subsequent structural health monitoring. The general test plan, sensor placement, and measured responses are described. The static deflection, the stress of the main girder, and the rotation angle at the beam end are used to evaluate the static performance of the bridge. The natural frequencies and mode shapes are used to assess the dynamic performance of the bridge. A FEMU framework that utilizes displacement assurance criterion (DAC) and frequency to construct a single-objective function is proposed to update the initial finite element (FE) model of the bridge. The results show that the deflection to span ratio is 1/1016 (less than1/1000), and the rotation angle at the beam end under live load is 0.032 ‰ rad (<1‰), indicating that the bridge has sufficient vertical stiffness and excellent riding comfort. The stress of the main girder is smaller than the material yield strength, indicating that the bridge has sufficient load-bearing capacity. All the requirements allowing the bridge to start service have been met. The updated FE model shows that the DAC performs better than the displacement and provides more accurate updating results. The updated FE model can well reflect the static and dynamic characteristics of the actual bridge and can be used as a baseline FE model for subsequent studies.

Kinetic time-curves can classify individuals in distinct levels of drop jump performance

ABSTRACT This study examined whether analysing kinetic features of drop jumps (DJ) as one-dimensional biomechanical curves can reveal specific patterns that are consistent and can cluster DJ performance. Hierarchical clustering analysis on DJ from 40 cm data performed by 128 physically active male participants (23.0 ± 4.5 yrs, 1.84 ± 0.07 m, 79.1 ± 10.8 kg) was performed on the derived time-normalised force, power and vertical stiffness curves to unmask the underlying patterns and to explore the dissimilarities identified from the subgroup (cluster) analysis. Results revealed poor, average and top DJ performers. Top performers exhibited larger peak force, power and vertical stiffness compared to the other two groups, and the poor performers had lower values compared to the average performers (p < .05). The time curves of force, power and vertical stiffness exhibited between cluster dissimilarities from ~25% to ~70%, and ~20% to 40% plus ~55% to 70% from the beginning of the ground contact, respectively. The force and power time-curves distinguished DJ ability similarly since they shared 69% of the cases in the top performers’ cluster. The content of cases (membership) for vertical stiffness was different from the membership for the force and power time-curve clusters. In conclusion, stiffness should be considered during plyometric training, but does not distinctly define DJ performance.

Numerical and experimental study of mechanical behaviors of the steel-confined rubber bearing

The conventional laminated rubber bearing is primarily for the horizontal seismic input. To achieve three-dimensional seismic isolation, the horizontal laminated steel plates in rubber bearings are replaced by externally confined steel plates, which is the steel-confined rubber bearing (SCRB). The external steel cover effectively increases the stability of the rubber bearing, while acting as a U-shaped steel cover and improving the energy dissipation capacity of the isolator. The mechanical properties of the SCRBs were investigated based on finite element analysis and experiments. The test and numerical results show that the SCRB has a low horizontal and vertical stiffness, while the external steel cover provides additional damping for the rubber isolator. The modified Bouc-Wen model was introduced to simulate the horizontal and vertical force–displacement hysteresis relationship of the SCRB. Based on FE model simulations, the effects of area coverage, quantity and length of steel cover on vertical stiffness, horizontal stiffness and equivalent damping ratio of the SCRB were analyzed in detail. A design procedure of the SCRB based on the stiffness is proposed. Finally, the effectiveness of the SCRB on reducing horizontal and vertical seismic responses is validated using a single-degree-of-freedom system.

Design and Experimental Characterization of a Push-Pull Flexible Rod-Driven Soft-Bodied Robot

Soft robots with a well-balanced performance in terms of dexterity, accuracy, and payload have a great potential for application. Balancing safe human-robot interaction with operation performance enables the use of soft robot in biomedical fields, among others, such as surgery, rehabilitation and elder care. In this letter, we present a rod-driven soft robot (RDSR) where the flexible rods embedded in the silicone-based body provide a double push-pull actuation, to satisfy the needs of balanced performance. The RDSR can realize multi DOFs movement with elongation, contraction and bending. For trajectory tracking, Gaussian process model enables RDSR to achieve more accurate motion control with an RMSE within 2.8 mm compared to the constant curvature model with that within 10.8 mm. Comparative experiments demonstrate that the workspace, vertical and lateral stiffness of the RDSR are up to 5, 2.6 and 5.2 times that of an analogous tendon-driven soft robot (TDSR), respectively. Additionally, the RDSR possesses the ability, that the TDSR does not have, to actively apply pushing perpendicular to an inclined plane. Based on numerical Jacobian matrix, the maximum force along target direction is greater than 4 N for a 30 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> plane. Furthermore, pick-and-place tests validate that our soft robot, with large workspace, precise and steady motion, is capable of conducting object manipulation tasks.

Estimation of running biomechanical parameters using magneto-inertial sensors: a preliminary investigation

Many runners perform training sessions outdoors and on varying surfaces (e.g., track, paved path, trail). Training surface has been shown to influence running spatiotemporal measures and stiffness [1]. However, applied research in understanding training surface influence has been limited by lack of robust methodology to capture biomechanics in-the-field. The increasing availability of wearable magneto- inertial sensors (MIMUs) is now making it possible to perform in-field assessment of running biomechanics [2]. Validation of new inertial-based methods is vital to widespread field use. In this study, we compared inertial-based methods for running biomechanical analysis and against gold-standard stereo-photogrammetric system (SP). Ten recreational male runners (age: 32.3 ± 10.0 years) were enrolled and asked to run on a treadmill at 14 km/hr for 8 trials lasting 6 minutes. We simulated changes in surface in a controlled lab setting by using 8 different footwear conditions. Participants were instrumented with MIMUs (mod: Opal v2, APDM, Portland, USA; fs=200 sample/s) attached on the pelvis (L5) and the instep of both feet, and retroreflective markers on heels, toes, and each MIMU (recorded with a 9-camera Vero system, Vicon, Oxford, UK; fs=200 sample/s). The estimated relevant biomechanical parameters included: stride/stance/swing duration, stride rate, vertical oscillations of the center of mass (CoM), and vertical/leg stiffness. Gait events (initial and final contacts) were estimated using a modified version of the MIMU-based method proposed by Benson et al. [2]. CoM vertical displacement was estimated as the vertical component of the L5 MIMU trajectory. Vertical and leg stiffness were computed starting from CoM displacement, stance interval, and swing interval [3]. For each participant and trial condition, errors with respect to SP were computed (80 values for each parameter) and root mean squared errors (RMSE) across participants and conditions were then calculated. In addition, a Bland-Altman analysis was used to quantify the agreement between MIMU and SP outcomes in terms of 50% limits of agreement interval (LoAI). Differences between MIMU-based and SP-based parameters over all the runners are reported in Table 1. Results showed high accuracy especially in the estimation of stride duration, stride rate and CoM vertical displacement. The level of uncertainty associated to each biomechanical variable, as provided by the LoAIs, can be used to detect differences in surface conditions (footwear conditions). Future analysis and development of field methods will investigate the influence of unconstrained movements (outdoor, no treadmill) in addition to varying surface conditions and the influence of running speed on inertial-based method accuracy.