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1、 Structure and Infrastructure Engineering Maintenance, Management, Life-Cycle Design and Performance ISSN: 1573-2479 (Print) 1744-8980 (Online) Journal homepage: http:/ Parametric study of seismic performance of super- elastic shape memory alloy-reinforced bridge piers Bipin Shrestha & Hong Hao To c
2、ite this article: Bipin Shrestha & Hong Hao (2015): Parametric study of seismic performance of super-elastic shape memory alloy-reinforced bridge piers, Structure and Infrastructure Engineering, DOI: 10.1080/15732479.2015.1076856 To link to this article: http:/dx.doi.org/10.1080/15732479.2015.107685
3、6 Published online: 01 Sep 2015. Submit your article to this journal Article views: 70 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http:/ Download by: University of Illinois at Urbana-Champaign Date: 10 February 2016, At: 07:48 DownloadedbyUniv
4、ersityofIllinoisat Urbana-Champaign at 07:4810February 2016 Structure and InfraStructure engIneerIng, 2015 http:/dx.doi.org/10.1080/15732479.2015.1076856 Parametric study of seismic performance of super-elastic shape memory alloy-reinforced bridge piers Bipin Shrestha and Hong Hao department of civi
5、l engineering, curtin university, Bentley, australia ABSTRACT One of the important measures of post-earthquake functionality of bridges after a major earthquake is residual displacement. In many recent major earthquakes, large residual displacements resulted in demolition of bridge piers due to the
6、loss of functionality. Replacing the conventional longitudinal steel reinforcement in the plastic hinge regions of bridge piers with super-elastic shape memory alloy (SMA) could significantly reduce residual deformations. In this study, numerical investigations on the performance of SMA-reinforced c
7、oncrete (RC) bridge bents to monotonic and seismic loadings are presented. Incremental dynamic analyses are conducted to compare the response of SMA RC bents with steel RC bents considering the peak and the residual deformations after seismic events. Numerical study on multiple prototype bridge bent
8、s with single and multiple piers reinforced with super-elastic SMA or conventional steel bars in plastic hinge regions is conducted. Effects of replacement of the steel rebar by SMA rebar on the performance of the bridge bents are studied. This paper presents results of the parametrical analyses on
9、the effects of various design and geometric parameters, such as the number and geometry of piers and reinforcement ratio of the RC SMA bridge bents on its performance. ARTICLE HISTORY received 12 March 2015 revised 9 July 2015 accepted 15 July 2015 KEYWORDS Shape memory alloy; residual displacement;
10、 reinforced concrete; bridge piers; incremental dynamic analysis 1. Introduction Reinforced concrete (RC) bridges designed to current seismic codes in the regions of high seismicity are susceptible to severe damage during large earthquakes, leading to the possibility of large residual displacements.
11、 During major earthquakes such as the Northridge 1994, Kobe 1995, Duzce 1999 and other events, it was found that bridge structures sustained high residual drifts rendering the bridge to be unserviceable. Consequently, post- disaster rescue and relief operations were severely affected. The principal
12、factor leading to the loss of serviceability was residual strains in steel reinforcement bars after an earthquake resulting in larger residual inclination of bridge piers. During the 1995 Kobe earthquake, 88 bridge piers along the Hanshin expressway were demolished because of the large residual incl
13、ination even though some of those piers had experienced only light damage (Fujino, Satoko, & Abe, 2005). As a result, there is a consensus among the engineering practitioners that the residual displace- ment has a greater significance in the overall structural perfor- mance of the infrastructure und
14、er earthquake loading. As bridges are the key components in the transportation net- work for providing emergency services following an earthquake, it is necessary to minimise the loss by enhancing the performance of the bridges. During strong earthquakes, steel reinforcements are expected to endure
15、large plastic deformations under severe shakings to dissipate seismic energy. This inevitably leads to sig- nificant residual deformation that could make bridge structures unserviceable or unsafe. To address these problems innovative design methods capable of re-centreing after an earthquake event a
16、re being explored since last few decades. One of such innovative methods is using a relatively new material for civil infrastruc- ture system, super-elastic shape memory alloy (SMA) as rein- forcement on structures. SMAs are able to undergo large strains and still recover their shape through either
17、heating (shape- memory effect) or stress removal (super-elastic effect) (Wilson & Welsolowsky, 2005). In general, SMAs exhibit two distinct crystal structures or phases. These phases are martensite, with the ability to completely recover residual strains by heating, and austenite, with nominally zer
18、o residual strain when unloaded without the application of heat. Super-elastic behaviour of SMA would be beneficial in many ways particularly for civil engineering appli- cations, especially to reduce permanent deformation of structural components. Previous studies have highlighted that super-elasti
19、c SMA could be an ideal alternative material for use as reinforcement in RC structures to reduce the large residual deformation. Several studies have been conducted in recent years using the super-elas- tic behaviour of SMA by placing it in plastic hinge locations of RC structures to mitigate the la
20、rge residual deformations after strong earthquake shakings. Saaidi and Wang (2006) explored the effectiveness of using the super-elastic SMA bars at plastic hinge regions of RC columns by conducting shake table exper- iments. Youssef, Alam, and Nehdi (2008) utilised SMA in the CONTACT Bipin Shrestha
21、 bipin.shresthapostgrad.curtin.edu.au 2015 taylor & francis 2 B. SHRESTHA ANd H. HAO DownloadedbyUniversityofIllinoisat Urbana-Champaign at 07:4810February 2016 plastic hinge region of RC beam column joints. Saiidi, O Brien, and Sadrossadat-Zadeh (2009) compared the responses of SMA- reinforced RC c
22、olumn with normal concrete and engineered cementitious composite (ECC) to steel RC column under cyclic loading test. Cruz and Saiidi (2011) investigated the seismic performance of a large-scale four-span RC bridge incorporating innovative plastic hinges consisting of super-elastic SMA and ECC using
23、shake table tests. The above studies experimentally validate that SMA reinforcement in critical regions of concrete structures could significantly reduce the earthquake-induced damages and dissipate an adequate amount of energy. Billah and Alam (2012), Zafar and Andrawes (2012) numer- ically investi
24、gated hybrid SMA column with SMA bars at the plastic hinge regions as non-corroding reinforcement for ductile RC structures. Billah and Alam (2014) extended their study by assessing the seismic performance of SMA RC bridge piers using fragility function. Tazarv and Saiidi (2013, 2015) investigated t
25、he performance of concrete columns with super-elastic SMA bar and the effects of key mechanical properties of one of the most commonly used SMA, Nickel Titanium (NiTi), bars on seismic performance of SMA RC bridge piers. Roh and Reinhorn (2010), Nikbakht, Rashid, Hejazi, and Osman (2015) investigate
26、d on the applications of SMA bars in precast segmental bridge columns to improve the hysteretic energy dissipation of the columns. The above researches demonstrate that super-elastic SMA could be a strong contender for use as reinforcements at plastic hinge regions of RC structures, which are prone
27、to experience sig- nificant damages during strong seismic events with large residual deformation. However, the conclusion based on investigation of a single RC column, usually of small scale may not give a conclu- sive result. The performances of realistic RC bridge bent having different geometries,
28、 and the numbers of piers subjected to a suite of earthquake ground motions are inexistent. Moreover, previous studies have not focused on parametrically studying the influence of the replacement of steel reinforcement with SMA reinforce- ment on the performance of the bridge bents. Super-elastic SM
29、A bars have different characteristics compared to conventional steel reinforcement. For example, the modulus of elasticity SMA is in general 1/2 1/5 of steel reinforcement and yield strain is sig- nificantly higher than steel reinforcement. This variation in the properties of two types of reinforcem
30、ents demands significant attention in order to better understand the performance of bridge piers with SMA-reinforced piers compared to conventional piers. Presently, there are not any guidelines provided by the liter- atures on replacement of steel by SMA reinforcement. Previous studies mostly compa
31、red the performance of SMA RC bents with steel RC bents with either lower or similar moment capac- ity. However, this may result in higher peak drift of the SMA- reinforced bridge piers compared to conventional steel-reinforced pier due to lower modulus of elasticity of SMA bars. Previous studies ha
32、ve not parametrically studied the effect of reinforce- ment ratio of SMA bars on performance of the SMA bridge bents. In this study, intensive analyses are conducted to compare the responses of concrete bridge bents with SMA reinforcements and conventional steel reinforcements subjected to different
33、 earthquake excitations. The behaviour of the SMA piers under the monotonic loading is evaluated and compared against steel- reinforced piers. Furthermore, incremental dynamic analyses are used to investigate the performance of super-elastic SMA RC bents under seismic loading. To give a generalised
34、observation, 12 models with variations in geometry, the numbers of piers in a bridge bent and varying super-elastic SMA rebar ratio are analysed. To reduce the cost of the bridge, SMA reinforcements are placed at critical plastic hinge regions of bridge piers and connected to steel reinforcement usi
35、ng couplers. For this purpose, in this work, numerical models are devel- oped using fibre-based element model on Seismostruct. The accuracy of the numerical models on predicting the response of SMA-reinforced bridge piers is first validated by comparing the results with the experimental shake table
36、data of a bridge pier with SMA reinforcement (Saiidi & Wang, 2006). The contribu- tion of the present study is to (1) compare the performance of the prototype bridge bents with steel and SMA reinforcements in terms of damage progression, peak deformations, residual deformation and energy absorption
37、capacity, and (2) compare parametrically the performance of SMA RC bents with varying reinforcement ratio to steel RC bents. 2. Validation of numerical model In order to achieve realistic results, validation and calibration of the numerical model are essential. In this study, to validate the numeric
38、al model for inelastic dynamic time history analy- sis, experimental study by Saiidi and Wang (2006) on a large- scale RC column conducted at the structure laboratory of the University of Nevada, Reno, is used. The experiment is briefly described in this section. A RC column scaled to 1/4 with SMA r
39、einforcements in the plastic hinge region was tested on a shake table. In the experiment, NiTi bars, 356-mm long, were used as longitudinal reinforcement in plastic hinge area. Details of the experimental column are presented in Figure 1. The mechanical properties of the SMA bars along with the rein
40、- forcement and concrete are presented in Table 1. An axial load of 624 kN was applied, corresponding to an axial load index (ALI) of .25, where the ALI is defined as the ratio of the axial load and the product of the gross column section and the specified concrete compressive strength. The NiTi bar
41、s provided the reinforcement in the lower 254 mm of the column. The column was subjected to a synthetic ground motion compatible to the Applied Technology Council 32 (Applied Technology Council 1996) for medium soil (ATC-32-D). Peak ground acceleration (PGA) of the motion was .44 g. The specimen was
42、 subjected to a series of scaled motions, the amplitudes of which were progressively increased. The specimen was subjected to 11 runs of the ground motion excitation, with amplitude normalised to 15% for the first run to 300% for the last run of the ATC-32-D record amplitude. More detailed informati
43、on of the experimental tests can be found in Saiidi and Wang (2006). SMA model The NiTi rebar is usually based on the equiatomic compound of nickel and titanium. Beside the ability of tolerating large amounts of strain, shape-memory NiTi alloys show high sta- bility in cyclic applications and are co
44、rrosion resistant. They also have a moderate solubility range, enabling changes in com- position and alloying with other elements to modify both the shape-memory and mechanical characteristics. For commercial application and in order to improve its properties, a third metal STRuCTuRE ANd INfRASTRuCT
45、uRE ENgINEERINg 3 DownloadedbyUniversityofIllinoisat Urbana-Champaign at 07:4810February 2016 Figure 1. details of SMa rc column (Saiidi & Wang, 2006) (reproduced with permission). is usually added to NiTi. Although two metals (nickel and tita- nium) are processed identically, a slight increase in n
46、ickel content improves the mechanical behaviour of SMA by depressing the transformation temperatures and improving the hysteretic energy dissipation capacity. In order to realistically represent the NiTi reinforcement, one-dimensional uni-axial model for super-elastic SMA pro- grammed by Fugazza (20
47、03) following the constitutive relation- ship proposed by Auricchio and Sacco (1997), implemented on Table 1. Material properties for SMa rc column. Material Property Value unconfined concrete compressive strength (MPa) 43.8 Strain at peak stress (%) .002 tensile strength (MPa) 0 confined concrete c
48、ompressive strength (MPa) 43.8 Strain at peak stress (%) .0025 tensile strength (MPa) 4.38 Longitudinal steel Yield strength (MPa) 469 Youngs modulus (MPa) 1,99,000 Super-elastic SMa Modulus of elasticity 48,300 Seismostruct program is used in numerical simulations. This model is capable of describi
49、ng the force deformation relation- austenite to martensite starting stress, fsm (MPa) austenite to martensite 379 405 ship of super-elastic SMAs at constant temperature. The model finishing stress, ffm (MPa) is sufficiently accurate for the present study with respect to the temperature effects because unlike in other applications, SMA bars is not exposed to ambient temperature and are insulated by a thick layer of concrete. A schematic of force deformation re