Free-standing Columns Research Articles

Characterizing the free-vibration response of a two-span rocking bridge with free-standing columns

For accelerated bridge construction (ABC), replacing traditional emulative connections of precast elements with simpler discontinuities may lead to more resilient structures with reduced expected damages after strong seismic events. This paper comprises novel free-vibration tests of a 1:10 scale two-span rocking bridge with free-standing columns with proper geometrical and dynamic similarity. The two spans induced in the model the interaction between frames with different tributary masses, as would be expected for a realistic bridge. To excite the bridge uniformly, the experimental protocol consisted of forty-nine incremental sinusoidal ground motions that were interrupted, letting the bridge vibrate freely to rest. The results were compared with six analytical models. The results showed that the structure remained undamaged for the free-vibration tests after drifts up to 6 % and did not wobble unrestricted. The results were used to obtain the dynamic properties of the system and their variation to displacement increments. Construction imperfections induced the model to rock for all excitations, including low-intensity excitations, and to vibrate with periods different from those of theoretical equations at low displacements. This behavior was critical in the comparison between experimental results and the estimates from analytical models. These findings demonstrate that rocking bridges are a suitable system to control structural damage during seismic events despite the apparent variability of the behavior under realistic conditions. However, the design of these structures must account for the effects of construction imperfections at the rocking surface. The experimental results are openly available for download in the DesignSafe Data Depot using this DOI https://doi.org/10.17603/ds2-znfv-8t55.

Inelastic Behavior of Mortise-Tenon Jointed Traditional Timber Frame with Free-Standing Columns

ABSTRACT This paper aims to study lateral behavior of the semi-mortise-tenon (SMT) jointed frame with free-standing columns with elastic-plastic deformations in the traditional timber building. The frictional and compressive forces at contact interfaces of SMT connection are calculated through the volumes of elastic and yielding deformations perpendicular-to-grain, and the compressive force is analyzed considering the elastic and yielding deformations parallel-to-grain at the bottom of column. The elastic-plastic behavior of timber frame with SMT and column foot (CF) connections under different vertical loads is assessed. The results reflect that the main plastic deformation of the timber frame occurs at SMT connections perpendicular-to-grain, and the effect of the plastic deformations parallel-to-grain at CF of the timber frame on its lateral resistance is relatively small, the lateral resistance of the wood frame shows a trilinear characteristic. Moreover, the gravity load of the upper structure does not directly affect the plastic deformation perpendicular-to-grain at SMT connections—the SMT connection of the timber frame with a larger gravity load of an upper structure is more likely in the plastic stage than that of a smaller gravity load of an upper structure.

Modeling, fragility and risk assessment of ancient freestanding columns and colonnades

A novel methodology for the fragility and risk assessment of ancient freestanding monolithic columns and colonnades is presented. The proposed approach is based on a modeling that can be implemented in a general purpose seismic design software, thus avoiding time-consuming and/or complicated simulations. Furthermore, a novel performance-based fragility and risk assessment framework, tailored to the problem at hand, is presented. The paper first discusses the problem of modeling these structures as rocking systems using negative-stiffness rotational springs. For the fragility assessment, pertinent performance criteria and intensity measures are proposed. The examples discussed show the capacity of the proposed modeling to simulate a variety of column and colonnade ancient structures and to quickly provide accurately the fragility curves within a fully performance-based framework.

Numerical investigation of the contribution of metallic dowels to the stability of multi-drum columns

Remnants of Greek Temples are found all over the Mediterranean, surviving in most cases in the form of free-standing columns. In many cases the drums are placed on top of each other without any connection, whereas in some cases there exist metallic dowels between the drums. The aim of this work is to investigate the contribution of these dowels to the overall stability of multi-drum columns. For that, the paper studies numerically the complex 3D dynamic response of multi-drum columns with dowels between the drums, by using the FE code MARC. The studied columns are part of the colonnade system of the ancient Messene Gymnasium in Greece. In the 3D models, which are based on archaeological data, special attention is given to the modelling of the metallic dowels which were used to connect adjacent drums. The columns are subjected to sinusoidal base excitations having different acceleration amplitudes and different frequencies.

Cultural perspectives on the Hopewell Rocks: Investigating community values in a geotourism context

Our research explores human connections to shoreline rock formations at Hopewell Rocks Provincial Park, New Brunswick, and the ways in which people experience the site. The Hopewell Rocks are a group of sea stacks and arches on the shore of the Bay of Fundy that are visited by more than 250,000 geotourists annually. One of these formations, Elephant Rock, is well known in the province as it is featured on the New Brunswick health card.
 Sea stacks are freestanding columns of rock created by shoreline erosion. These striking formations are dramatic and mysterious; many are consequently popular tourist destinations worldwide. Sea stacks are unstable by nature and visiting them poses some risk. This research represents an initial attempt to formally characterize the perceptions, beliefs, and connections that humans hold to these rock formations.
 This study involves a publicly advertised research survey and interview series to collect quantitative and qualitative data, reaching beyond a single research method to capture a comprehensive result. The survey is a multiple-choice and short answer questionnaire administered through Qualtrics, an online survey platform, which covers topics of connection to the land, safety, aesthetics, and education. We received 248 survey responses that present diverse perspectives ranging from the pragmatic to the spiritual. Preliminary data analysis shows support for the idea that New Brunswickers have a strong positive connection to the Hopewell Rocks. The results of this study will inform future related research on evaluating the risk to public safety posed by geotourism at this and similar sites.

Lateral performances of traditional wooden frame with loose penetrated mortise-tenon connection and column foot models

Traditional wooden structures in China have free-standing columns on top of stone bases and the beams and columns connected by mortise-tenon joints. Many of them have been in service for hundreds of years withstanding many seismic events, and yet their performances against lateral loadings are not clear. This paper studies the behavior of a wooden portal frame with penetrated mortise-tenon (PMT) connections and column foot (CF) connections under transverse load. An analytical model for a planar loose PMT connection is proposed based on the load-displacement relationship. The mechanical behavior of these loose connections with the friction-slip-contact mechanism is studied with clear evidences of negative stiffness in the lateral resistance of the wooden frame. The different contact states of the PMT and CF connections in the load resisting process are studied. Results indicate that the lateral performances of the wooden frame are dependent on the synergistic action of the PMT and CF connections. The lateral deflection mechanism of a wooden frame is strongly affected by the loose PMT connections and the P-Δ effect of the supporting columns.

Seismic fragility and intensity measure investigation for rocking podium structures under synthetic pulse‐like excitations

AbstractRocking podium structures (RPSs) refer to a wide class of structural systems in which the base storey consisting of freestanding columns that can uplift during seismic excitations. Due to the rocking response, the base storey can be considered as a base isolation system on the condition that a rocking overturn is prevented. In the present study, the seismic response of RPSs is assessed within a probabilistic framework. For this purpose, synthetic pulse‐like acceleration records are generated. The performance of several ground motion intensity measures in predicting the rocking response of RPSs with different superstructure's fundamental period, lateral displacement profiles and rocking column configuration are examined. The effect of these structural parameters on the rocking response is evaluated in terms of seismic fragility. Finally, the seismic behaviour of the rocking storey, as a seismic isolation technique, is evaluated by examining both the rocking stability and the seismic demand reduction of the superstructure simultaneously.

Experimental and numerical study of axially loaded reinforced concrete columns and frame columns under lateral impact loading

Pendulum impact tests were conducted on a reinforced concrete (RC) frame column and four RC free-standing columns. The effects of the axial compression ratio and reinforcement ratio on the impact resistance of the columns were compared using the dynamic time curves of framed and freestanding columns under impact. The test results show that for the same impact load, although the presence of axial loads can play a positive role (e.g., reducing the residual displacement), it may lead to more severe local damage. In addition, compared with free-standing columns, frame columns can be considered as a protective structure because of their greater lateral stiffness and stronger crashworthiness. The corresponding finite element models are developed, and the influence of the axial loads on the cross-section force responses under impact excitation was deeply explored. Axial loads can significantly affect the distribution of moment, shear force, and damage to the column.

Inversion of force lines in fiber-reinforced jammed granular material

Freestanding columns, built out of nothing but loose gravel and continuous strings can be stable even at several meters in height and withstand vertical loads high enough to severely fragment grains of the column core. We explain this counter-intuitive behavior through dynamic simulations with polyhedral rigid particles and elastic wire chains. We evaluate the fine structure of the particle contact networks, as well as confining forces and reveal fundamental intrinsic differences to the well-studied case of confining silos.Graphic abstract

Analysis of Rocking Behavior of Tang-Song Timber Frames under Pulse-Type Excitations

This paper investigates the rocking behavior of two free-standing columns capped with a freely supported superstructure in an effort to explain the seismic stability of Tang-Song timber frames subjected to pulse-type excitations. The geometric characteristics of the column determine the acceleration amplitude needed to create uplift of the rocking frame, which also affect the loss of energy during impact along with the mass ratio of the superstructure to the column. Two distinct rocking modes are analyzed according to whether the frame can be limited by the tenon-mortise joint. The expression that yields the minimum acceleration required to overturn the frame is derived within the limits of the linear approximation of the governing equation of motion. Different safety and overturning regions plotted on the stability diagrams indicates that the partially joint limitation may weaken the seismic behavior. The entirely limited frame will rock within the fixed amplitude caused by the joint gap and never topple down. Probability analysis results of the entirely limited frame suggest that a great majority of this type of traditional timber structures have excellent seismic capacity to resist the horizontal excitation.

Shaking table tests of a single-span freestanding rocking bridge for seismic resilience and isolation

Rocking philosophy has advantages to maintain a preferable post-earthquake serviceability as an alternative of seismic resistant systems. This article presents an experimental study on the seismic behavior of a rocking bridge with freestanding columns capped with a freely supported deck. A 1/10 scaled, single-span double-column freestanding bridge was constructed and tested on a shaking table. The experimental results showed that the bridge model could undergo large rocking with enough stability under earthquakes and presented excellent post-earthquake resilience after earthquakes with limited damage and negligible residual displacement. The rocking bridge model also exhibited expected isolation efficiency, which increases as the level of excitations becomes more severe. In addition, an analytical model based on multi-block rocking mechanisms was used to calculate the displacement response. Compared with the experimental results, this analytical model well predicts the peak displacement of the rocking bridge model.

Effect of Supplemental Hysteretic and Viscous Damping on Rocking Response of Free-Standing Columns

AbstractThis paper investigated the nonlinear, rocking seismic response of slender, free-standing columns when equipped along their sides (or at their pivoting points) with vertical energy dissipat...

Non-linear static behaviour of ancient free-standing stone columns

This work investigated the non-linear behaviour of ancient natural stone columns in the Mediterranean region made from multiple blocks or ‘drums’. A two-dimensional custom-made computational model based on the discrete-element method was employed. In the numerical model, the columns were represented as an assemblage of distinct blocks connected together by zero-thickness interfaces, which can open and/or close depending on the magnitude and direction of the stresses applied to them. Through non-linear static analysis, capacity curves and corresponding failure mechanisms of each of the studied models were obtained. The influence of different parameters (the number of drums, geometrical properties and imperfections at columns) was also assessed to observe their influence on the response of drum assemblies. The results of analyses revealed that rigid overturning is the main collapse mechanisms under uniform horizontal forces. A combination of rigid and shear failure mechanisms might also occur, depending on geometric characteristics and the choice of joint material properties. A higher displacement capacity was observed for columns constructed with a larger number of drums. It was also found that imperfections in the ancient free-standing columns have a significant influence on the lateral load resisting capacity. Therefore, structural analysis of undamaged columns may not represent the actual capacity of the columns due to their very sensitive and highly non-linear characteristics.

Efficiency of alternative intensity measures for the seismic assessment of monolithic free-standing columns

This paper deals with the dynamic response of a free-standing ancient column in the Roman Agora of Thessaloniki, Greece as a means to shed more light on the complex behaviour of rocking bodies under seismic excitation. Numerical analyses utilizing discrete element method were carried out with the use of multiple seismic records selected based on the disaggregation of the seismic hazard for the region of interest. To identify their impact on structural performance, earthquake Intensity Measures, such as Peak Ground Acceleration and Peak Ground Velocity are examined for the case of a column that sustained no visible permanent deformations during the Ms = 6.5 Thessaloniki earthquake of 1978. The analysis revealed a weak correlation of PGA and PGV with the response results and a significant influence of the mean frequency (fm) of the seismic motion. No coupling was found between the maximum displacement of the top during the oscillation and the permanent post-seismic deformations. The complementarity of both earthquake Intensity Measures in the structural vulnerability assessment is also depicted.

Examining the Dynamic Response of Classical Columns

Ancient monuments have often sustained severe damage due to earthquakes. The examination of their dynamic behavior can reveal their vulnerability to different dynamic excitations. Ancient temples consisting of classical columns are of particular interest, due to their architectural features and complex geometry. The dynamic response of short free-standing classical columns is investigated in this study. Two small scale marble columns of the same size but with a different number of drums are subjected to harmonic, random and earthquake excitations. The effect of their geometrical features on their dynamic behavior is examined. Numerical models based on the finite element method can provide reasonable estimates of the dynamic response of classical columns but cannot predict all the attributes of their actual dynamic behavior.

Freestanding loadbearing structures with Z-shaped particles

Architectural structures such as masonry walls or columns exhibit a slender verticality, in contrast to the squat, sloped forms obtained with typical unconfined granular materials. Here we demonstrate the ability to create freestanding, weight-bearing, similarly slender and vertical structures by the simple pouring of suitably shaped dry particles into a mold that is subsequently removed. Combining experiments and simulations we explore a family of particle types that can entangle through their non-convex, hooked shape. We show that Z-shaped particles produce granular aggregates which can either be fluid and pourable, or solid and rigid enough to maintain vertical interfaces and build freestanding columns of large aspect ratio ( $$>$$ 10) that support compressive loads without external confinement. We investigate the stability of such columns with uniaxial compression, bending, and vibration tests and compare with other particle types including U-shaped particles and rods. We find a pronounced anisotropy in the internal stress propagation together with strong strain-stiffening, which stabilizes rather than destabilizes the structures under load.

Mutual seismic assessment and isolation of different art objects

New developments of a research programme dedicated to the seismic performance assessment and base isolation protection of art objects are presented in this paper. The investigation field has been extended from massive marble statues, considered at first step of this study, to slender free-standing columns, and bronze statues with highly vulnerable geometrical portions. A semicircular marble column and an equestrian bronze sculpture located in the main hall of the Restoration Laboratories of the Opificio delle Pietre Dure Institute in Florence are examined as representative case studies of the two classes, respectively. Rocking and sliding effects are simulated in the time-history assessment analyses of both artefacts, carried out by introducing all simultaneous components of seismic action as input. The results show an overturning-related near-collapse response of the column, and a plasticization-induced collapse of the statue, at the maximum considered earthquake level. In view of the different material and structural characteristics of the two artworks and several other art objects and equipments situated in the same hall, a mutual advanced seismic protection strategy is adopted, consisting in the base isolation of the floor by means of double curved surface sliders. This retrofit measure guarantees completely undamaged response conditions of the column and the statue, without requiring direct interventions on the two artworks. At the same time, the base-isolated floor constitutes a highly protective support for the hi-tech equipments housed in the Laboratories, as well as for any other artefact to be placed on it in the future.

Seismic Vulnerability Assessment Form for Free-Standing Columns Based on a Simplified Numerical Analysis

ABSTRACTThis article describes the creation of a seismic vulnerability assessment form for free-standing columns, based on Discrete Element Method simulations. A broad range of column configurations, selected after archaeological research, was analyzed. Each soil-column configuration was tested with 56 artificial accelerograms in the range of peak ground acceleration between 0.2 and 0.8 g. Fragility curves were created for each configuration and used to quantify the effects of soil, and the slenderness, height, and number of drums of each column. The influence factors of all parameters were used in the assessment form to categorize the columns into vulnerability classes, according to their probability of collapsing when subjected to a certain level of seismic excitation. The proposed tool can be used for rapid, preliminary, seismic vulnerability assessment, without the need for further sophisticated calculations. Four ancient columns, which have survived earthquakes of known acceleration amplitude, were used to apply, test and validate the proposed assessment form.

A half-century of rocking isolation

The uplifting and rocking of slender, free-standing structures when subjected to ground shaking may limit appreciably the seismic moments and shears that develop at their base. This high-performance seismic behavior is inherent in the design of ancient temples with emblematic peristyles that consist of slender, free-standing columns which support freely heavy epistyles together with the even heavier frieze atop. While the ample seismic performance of rocking isolation has been documented with the through-the-centuries survival of several free-standing ancient temples; and careful post-earthquake observations in Japan during the 1940's suggested that the increasing size of slender free-standing tombstones enhances their seismic stability; it was George Housner who 50 years ago elucidated a size-frequency scale effect that explained the "counter intuitive" seismic stability of tall, slender rocking structures. Housner's 1963 seminal paper marks the beginning of a series of systematic studies on the dynamic response and stability of rocking structures which gradually led to the development of rocking isolation-an attractive practical alternative for the seismic protection of tall, slender structures. This paper builds upon selected contributions published during this last half-century in an effort to bring forward the major advances together with the unique advantages of rocking isolation. The paper concludes that the concept of rocking isolation by intentionally designing a hinging mechanism that its seismic resistance originates primarily from the mobilization of the rotational inertia of its members is a unique seismic protection strategy for large, slender structures not just at the limit-state but also at the operational state.

Experimental investigation of the seismic response of classical temple columns

Remnants of Greek Temples are found all over the Mediterranean, surviving in most cases in the form of free-standing columns. The drums are resting on top of each other without any connection, being considered susceptible to strong seismic shaking. Their seismic response is complex, comprising a variety of mechanisms, such as rocking of sliding of the drums relative to each other. This paper studies experimentally the seismic performance of such structures, aiming to derive insights on the key factors affecting the response. Physical models of such multi-drum columns were constructed at reduced scale and tested at the shaking table of the NTUA Laboratory of Soil Mechanics. The marble specimens were excited by idealized Ricker wavelets and real seismic records. The tested multi-drum columns were proven to be very earthquake-resistant. Even when subjected to the strongest motions ever recorded in Greece, their permanent deformation was minimal.