Behavior of Semi-Rigid Steel Connection for G+ 3 Unsymmetrical Structures under Consideration of Seismic Forces

Steel structures are simple composite unit having different structural members such as beams, columns are so connected to one another with assumptions that the connections are either pinned or rigid connection. Pinned or Rigid connections are usually assumed for joint and support which provide simplifications in structural analysis and design but they neglect the true behavior of joint. To get true behavior of any joint in the structure the semi-rigid type of connection has to be introduced in the joint by taking spring stiffness of joint in account.

To study the effect of axial restraints on the connection behavior at elevated temperature, a finite element model of a top-seat angle connection developed and results shown that an increase in axial restraints has increased connection capacity while the stiffness remains similar for low axial levels.

To estimate rationally the ultimate moment Mu of connection three simple failure mechanism considering bending & shear deformation effects of prying action on top angle & stiffness of the tension bolts formulation developed. [2.4] A. Pirmoz, E. Mohammadrezapour (2008)(4) Studied moment-rotation behavior of this type under combined moment and axial tension force. Several refined 3D finite element models were created and their accuracy is examined comparing by results of previous experimental studies. This study showed that axial tension force reduces connection rotational stiffness and moment capacity.

A method of estimating the ultimate moment capacity has been proposed for top-seat angle connections

In this paper Initial Stiffness of semirigid connections under linear assumption presented. The fixed end moments of semi-rigid beams under concentrated, uniform and linearly varying loads are obtained. The importance of semi-rigid connection on the internal forces of steel frames is discussed and shown that initial stiffness of semi-rigid connections mainly related to the bending stiffness of joints, thickness and locations of bolts.

Beam – ISWB 250 Column – ISLC225 FR with 3 mm gap. Bracing - TUB32322.6 Slab thickness – 175 mm

1.Dead load A]Self weight of member = Applied through software. B]Floor Load ► Self weight of slab = 0.175*25 = 4.375 kN/m ► Floor finishing & Ceiling finishes = 1.5 kN/m Total load= 4.375+ 1.5 = 5.875 kN/m >>6 kN/m 2. Live load = 2.5 kN/m 3. Earthquake loads:

As per design results:

• Deflection in semi-rigid reduces by[(106.758-15.270)/106.758*100] 85.7% as per table 15when compared with pinned connection results as shown in fig 5.4 for pinned connection & fig 5.6 for semi-rigid connection. • Deflection in Rigid connection reduces by[(106.758-10.442)/106.758*100]90.21% as per table 15when compared with pinned connection results as shown in fig 5.4 for pinned connection & fig 5.5 for rigid connection. • Deflection in semi-rigid connection increases by [(15.270-10.442)/15.270*100]31.61% as per table 15when compared with rigid connection as shown in fig 5.5 for rigid connection & fig 5.6 for semi-rigid connection.

• Deflection in semi-rigid reduces by[(106.768-14.877)/106.768*100] 86.06% as per table 15when compared with pinned connection results as shown in fig 6.4 for pinned connection & fig 6.6 for semi-rigid connection. • Deflection in Rigid connection reduces by[(106.768-11.811)/106.768*100] 88.93% as per table 15 when compared with pinned connection results as shown in fig 6.4 for pinned connection & fig 6.5for rigid connection.

• When deflection is compared in semi-rigid and pinned connection for both load cases, it is observed that decrease in deflection in semi-rigid connection is more in load case 6 as compared to load case 5. • Increase in deflection of semi-rigid connection is more in load case-5 is more as compared with load case 6. • As the semi-rigid connection gives realistic behavior of structure and as per above results the semi-rigid connection is acting more ductile in nature compare to rigid connection collapse time of flexural member will increase. • As the collapse time increases in connection it tends to provide more safety against the major lateral loads acting on structures like earthquake, wind forces, etc.

• As the pinned connection will be having free rotation at the joint the joint displacement in both external and internal column is very high as compare to rigid and semi-rigid connection. The difference in joint displacement in internal column (109) & external (110) column are same which about {[105.962-8.832]/105.962*100}=91.66% increase in is pinned connection when compared with the rigid connection. • The difference in joint displacement in internal column (109) & external (110) column are same which increases joint displacement about {[105.962-11.673]/105.962*100=88.99 % in pinned connection when compared with the semi- rigid connection. • External (110) and internal (109) column Joint displacement increases by{[11.673-8.832]/11.673*100= 24.33% in semi-rigid connection when compared with rigid connection which provided more flexible

• As the pinned connection will be having free rotation at the joint the joint displacement in both external and internal column is very high as compare to rigid and semi-rigid connection. The difference in joint displacement in internal column (109) & external (110) column are same which about {[105.972-10.506]/105.972*100}=90.08% increase in is pinned conned when compared with the rigid connection. • The difference in joint displacement in internal column (109) & external (110) column are same which increases joint displacement about {[105.972-11.529]/105.972*100}=89.12 % in pinned connection when compared with the semi- rigid connection. • External and internal column Joint displacement increases by {[11.529-10.506]/11.529*100}=8.87 % in semi-rigid connection when compared with rigid connection which provided more flexible connection than rigid connection which tends to provide long time service as well as safety.

• Beam-Column joint displacement is more in load case 6 as compare to load case 5 {[(105.972-105.962)/105.972]*100= 0.009%} which is about 0.009% more in load case 6. • Beam-Column joint displacement is more in load case 6 as compare to load case 5{[(10.506-8.832)/10.506]*100=15.93%} which is about 15.93% more in load case 6 when compared with load case-5 for internal column & {[(10.478-8.857)/10.478]*100= 15.47%} about 15.47% more in load case 5 when compared with load case 6 for external column when designed as rigid connection. • Beam-Column joint displacement is more in load case 5 as compare to load case 6 {[(11.673-11.529)/11.673]*100= 1.23%} which is about 1.23 % more in load case 5 when compared with load case-6 for internal column & {[(11.681-11.514)/11.681]*100= 1.42%} about 1.42% more in load case 5 when compared with load case 6 for external column when designed as semi-rigid connection. connections for use in seismic applications submitted by Rassati, Dr. James A. Swanson Associacao Brasileira De Normastecnicas. Projeto de estruturas de concreto –Procedimento. – NBR 6118, Rio de Janeiro, 2003. Behavior of bolted top & seat angle connections under combined axial tension and moment loading submitted by Pirmoz, E. Mohammadrezapour (2008). Effect of Axial Restraints on top-seat angle connections at Elevated Temperatures submitted by Leong SiongHean, N.H.RamliSulong, Mohammed Jameel Haach, V. G. Analise teorico-experimental dainfluencia da força normal emnos de portico externosdeconcretoarmado. 2005. 159p. Dissertaçao (MestradoemEngenharia de Estruturas) – EscoladeEngenharia de Sao Carlos, UniversidadedeSao Paulo, Sao Carlos, 2005 Initial stiffness of Beam to column connections and structural internal force analysis submitted by Wang Yan, Liu Xiuli, Li Jianfen. Modified three parameter power model to predict moment-rotation curve of top and seat angle connection submitted by Ali Ahmed & Norimitsu Kishi. Prediction of moment-rotation characteristics of top-seat angle bolted connection incorporating prying action submitted by Ali Ahmed. The study of behavior of partially restrained connections under the effect of seismic load for top & seat angle connection submitted by Praveen Biradar, Dr. M.M. Awati

Assistant Professor, JSPM‘s ICOER, Wagholi, Pune