Experimental Studies of Failure Behavior and Strength of H Beams with Stiffened Web Openings under Compression and Bending Loads

,,

(1 Key Laboratory of High Performance Ship Technology of Ministry of Education,Wuhan University of Technology, Wuhan 430063,China;2 China Ship Development and Design Center,Wuhan 430064,China)

Experimental Studies of Failure Behavior and Strength of H Beams with Stiffened Web Openings under Compression and Bending Loads

ZHAO Ying-jiang1,YAN Ren-jun1,WANG Hong-xu2

(1 Key Laboratory of High Performance Ship Technology of Ministry of Education,Wuhan University of Technology, Wuhan 430063,China;2 China Ship Development and Design Center,Wuhan 430064,China)

Steel H beams with web openings are widely used as flexural members in ships,aircrafts, and offshore structures.In spite of numerous papers in the literature on beams with web openings subjected to web crippling,the effect of stiffened web openings subjected to plate buckling has not been exhaustively examined.Hence a detailed experiment study involving six specimens was undertaken to investigate the failure behavior and ultimate capacity load of H beams with stiffened web openings. The results show that the wavelength and quantities of the buckling waves were modified by the hole.This study can be used in practical structures with similar geometric features.

H beams;web openings;buckling waves;failure behavior; ultimate capacity load

0 Introduction

Opening H beams are used to lighten the ship,aircraft and make a way of access for air, pipeline or cable in ship and offshore structures.The presence of the openings(perforations) will cause structural discontinuity,stress redistribution and declining of ultimate bearing capacity.The girders and beams in ship and offshore structures are usually subjected to longitudinal thrust and vertical pressure.Under such combined loads,the behavior of the opening H beams is hard to be realized and the influence of related parameters become complex.

Thin plates with holes,which were primarily motivated by the design needs of the aerospace industry in early studies[1-2].Critical load was reduced and axial force in the plate strips adjacent to the hole was concentrated due to the existence of hole.Further study extended to beam with web openings[3-4].The parameters such as hole sizes,positions and shapes influencing the web crippling behaviors of opening beams are discussed and analysized.It is interesting that the presence of hole can either decrease or increase the critical elastic buckling stress andchange the length and quantity of buckled half-waves[5-6].

It is worth mentioning here that all the relevant researches above on H beams are subjected to web crippling behaviors.It is only one of typical collapse patterns that are classified into six groups by Paik[7],the collapse of the stiffened panel occurs at the lowest value among the various ultimate load calculated for each of the collapse patterns.In these situations,an appropriate cutout strengthening method is adopted to improve the ultimate load of H beams. Hence,H beams can avoid web crippling if the stiffeners are strong enough.However,the kind of experiment has not been carried out until now.Herein,in this paper,the detail failure behavior of H beams with stiffened web openings is investigated.On the basis of changing the hole positions we will explain the influence on failure behavior of H beams subjected to buckling or collapse of plate.

1 Strength experiment

In order to provide sufficient stiffness and to avoid web crippling,the basic geometry and notations of the specimens are shown in Fig.1.The specimens are composed of plating(333 mm× 10 mm×3 000 mm),stiffener web(240 mm×6 mm×3 000 mm)and stiffener flange(80 mm× 8 mm×3 000 mm).Location of the hole in stiffener web can be seen in Tab.1.The specimens are divided into series 1 and series 2 based on the location of the hole(see Tab.1).The behavior of the H beams subjected to compression and bending loads were observed.

Fig.1 Dimensions of the specimen

1.1 Specimen and equipment

The test specimens were fabricated using hot-rolled steel plating of Q235 which were most commonly used in ship hull building.The plates were cut by CNC plasma cutting technology.Weld uses manual arc welding,and the corresponding welding material is V840 electrode.One week was allowed for cooling in order to minimize the effect of initial distortion caused by excessive heating and to keep the residual stress minimum.

Tab.1 Hole location

To analyze the limit behavior of opening H beams subjected to compression and bending loads,an original experiment setup has been developed.An overview of the test rig is shown in Fig.2.Longitudinal thrust was controlled by MTS electro-hydraulic actuator with a capacity of 500 kN,the electro-hydraulic actuator could transfer hydraulic energy to mechanic energy and control the load accurately with a displacement sensor inside.Compression load was applied to the neutral axis of the specimen.In the vertical direction,bending load was simulated by five concentrated forces which were provided by hydraulic jacks with a capacity of 200 kN for everyone.Low carbon steel circular shafts were introduced at both end of the specimen and reaction frame to constraint the displacement and allow rotation of the end of the specimen. The electronic dial indicator was set to monitor the deflection of the middle of the specimen and strain gauges to monitor the strains of the specimen in the process of loading.A sectional view of the testing rig showing the details of load application is given in Fig.2.

The existence of the opening would result in the stress concentration of the plates near the hole,the stress level near the hole would reach the yield stress quickly.To improve the local buckling of the specimen of the perforated plates,we can adopt an appropriate cutoutstrengthening method and welding progress from Paik[7].The strengthening stiffener combined two parts,one was a plate with thickness of 6 mm and width of 300 mm is symmetrically welded to the perforated plate at their circular intersections after being rolled into a ring,another was a rectangular flat plate with a slotted hole that has the same size of the opening in the web,the plate was welded to the web with two circles being concentric.The welding is finally carried out along the inner edge and the four outer edges of the flat stiffener.

Fig.2 Overall and detail view of the test rig

1.2 Test procedure

All specimens were tested with two ends simply supported on the reaction frame.Before testing,the specimen should be positioned accurately to guarantee both compression load and neutral axial collinear.To ensure the safety and running well of the test,a small load of compres-sion load and bending load was applied and released before formal loading,respectively.Observe whether the instrument reading is in the normal level.

Compression load were applied to the neutral axial of the specimen firstly.Load level increased to 450 kN and with the compression load maintained constant at this level,the specimen wsa tested to failure by gradually increasing the vertical pressure.Reading of the electronic dial indicator and strain gauges were recorded for each increment of load.Buckling behavior of the specimen could be analyzed from the load-deflection curve or the load-strain curve obtained from the computer output.

2 Test results and discussions

2.1 Observations

As mentioned above,an appropriate cutout-strengthening method and welding progress were taken to avoid web crippling and improve the bulking capacity of the specimens.The buckling or collapse behavior of web did not occur in the test process.The results of failure modes of the specimens are shown in Fig.3 and Fig.4.As can be seen in Tab.1,BG-4,BG-5, and BG-6 were the specimens with hole at the edge of the web.For these specimens,similar buckling initiated at the mid-span of the plate.The initial buckling was followed by global buckling and the local buckling waves deepened at the same time.Fig.3 shows the specimens with hole at the mid-span of the specimens.As it is shown by red arrows in Fig.3,for BG-1 double buckling lobes occurred at the plate close to both sides of web opening,one buckling lobe occurred at the plate close to one side of web opening in BG-2,one buckling lobe occurred at the plate just below web opening in BG-3.

Fig.3 Failure mode of test specimens(a)BG-1;(b)BG-2;(c)BG-3;(d)BG-4;(e)BG-5;(f)BG-6

The following observations can be highlighted based on the above curves:

(1)The previous research[8-9]has indicated that the global buckling mode and local buck-ling mode are sensitive to the position of holes and local buckling mostly occurred at zone adjacent to hole.However,due to the stiffened structure of the web opening,the influence to the failure mode are local buckling modes of the plate other than global buckling modes of the specimens.

(2)For specimens with stiffened web opening at the edge of the web,the local buckling modes were similar with each other.

(3)For specimens with stiffened web opening at the mid-length of the web,as the vertical position of web opening varied,quantities and half wavelength of local buckling lobes were different.

2.2 Load capacity of the specimens

As mentioned earlier,the present specimens were subjected to compression and bending loads.The variation of vertical mid-span displacement is incredibly small in the step one(less than 1 mm).In each of these figures,only the vertical loads and the corresponding vertical displacement are plotted.Experimentally obtained load-displacement curves for series 1 and series 2 are summarized in Figs.4 and 5,respectively.

It is obviours that the ultimate capacity of specimens in series 2 are approximately in the same level of 365 kN,failure occurred around 97%,101%and 105%of the ultimate capacity of specimens in series 2 for specimen BG-1,BG-2 and BG-3 respectively,the effects were smaller than specimens subjected to web crippling.Combined with the corresponding failure mode in Fig.2 and Fig.3,we believe that the local buckling wave mode of the plate is directly related to the ultimare capacity of H beams.

Fig.4 Load-displacement curves for series 1

Fig.5 Load-displacement curves for series 2

As to the similar specimens in Konstantinos[10],a significant and sudden drop of load occurred directly after reaching the ultimate load capacity.This phenomenon did not occur in the experiment process,the reason is that the collapse patterns have been changed due to the existence of the stiffened web openings that can avoid web crippling behavior.

3 Conclusions

The present paper summarizes detail phenomena of six H beams with stiffened web open-ings in order to extract the relationship between the buckling wave modes of the plates and ultimate capacity loads under compression and bending loads.The results of the current study can be summarized as follows:

(1)The cutout-strengthening method and welding progress in this paper can avoid web crippling effectively.The failure behavior begins from the local buckling of the plate in the mid-span of the specimen.

(2)The local buckling wave modes of the plates were quite dependent on the opening location especially when opening locating at the adjacent region of the buckling wave.

(3)The local buckling wave modes have an important impact on the ultimate capacity loads.

(4)More work needs to be done in this research field to explore the relationship between the buckling wave modes of the plates and ultimate capacity loads under compression and bending loads.

Acknowledgements

The authors would like to thank Mr.Jun Ke and Geng Xu and Ms Jing Lin from Wuhan U-niversity of Technology for their help.

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腹板开孔的H型梁在压弯载荷下的失效行为和强度试验研究

赵应江1，严仁军1，王红旭2

（1武汉理工大学 高速船舶工程教育部重点实验室，武汉 430063；2中国舰船研究中心，武汉430064）

腹板开孔的H型钢梁在船舶，航空器和海洋平台结构作为受弯构件被广泛运用。已有众多文献报道过关于腹板开孔梁遭受腹板卷曲破坏的情况，但腹板开孔加强遭受面板屈曲的情况未有详尽调查。因此文中开展6组试件的试验研究来调查腹板开孔的H型梁的失效行为和极限承载力,结果显示开孔影响了试件屈曲波的长度和数量。该研究结果可用于几何尺寸相似的实际结构。

H型梁；腹板开孔；屈曲波；失效行为；极限承载力

U661.72

:A

赵应江（1989-），男，武汉理工大学交通学院博士研究生；

U661.72

A

10.3969/j.issn.1007-7294.2016.03.008

1007-7294（2016）03-0315-08

严仁军（1962-），男，武汉理工大学交通学院教授/博士生导师。

Received date：2015-09-21

Foundation item:Supported by Fundamental Research Funds for the Central Universities(WUT:2016IVA009)

Biography：ZHAO Ying-jiang(1989-),male,Ph.D.student of Wuhan University of Technology,E-mail:

zhao_yingjiang@163.com;YAN Ren-jun(1962-),male,professor/tutor.