Development of Precast RC Shear Wall Systems & Evaluation of their Lateral Load Resistance
CSIR-CBRI
IMG

Rapid urbanization and population rise around the world has triggered the demand for precast structures, attributed to their speedy, safe, sustainable and efficient construction methodology. These features have established precast construction as one of the most promising construction technology in the near future. However, previous earthquakes demonstrated the poor seismic performance of precast structures, which is much dependent on the efficacy and strength of the connections provided between the joints of precast panels. 

Thus, it is of utmost importance to improve the joint connection details and deploy seismic resisting features in precast buildings, such as the provision of precast shear walls. Load transfer mechanism and ductility offered by the joint connections play a key role in determining the overall seismic performance of precast structures, thus connections require proper design for adequate transfer of seismic forces between the precast panels.

Currently available codes mainly recommend steel connections, mechanical devices, shear keys, bolts, welding, dowel bars, etc. as a method of connections for precast walls. Another issue that limits the acceptance of precast shear walls in the construction industry is the laborious process of transportation and installation due to their heavy mass. The concern can be addressed by the development of a hollow precast shear wall system, also known as composite walls or sandwich walls. Sandwich systems are also advantageous for tall precast walls, where the weight of the precast panel exceeds the limit of the load-carrying capacity of cranes available. 

Keeping this in view, the 3D-Concrete, Printing Group at CSIR-Central Building Research Institute (CSIR-CBRI), Roorkee, carried out extensive experimental investigations and numerical studies on precast RC shear walls.

The study includes experimental and numerical investigations on (i) displacement controlled quasi-static reversed cyclic lateral load test on Precast RC Hollow Core Wall (PHCW) and (ii) displacement controlled quasi-static reversed cyclic lateral load test on precast RC wall-column connected through loop bar connection (PWCL). The results of lateral load tests are interpreted based on several key aspects pertaining to RC walls like damage pattern, failure mode, lateral load carrying capacity, stiffness, drift, ductility, response reduction factor and energy dissipation. To compare the effectiveness of precast RC shear walls, numerical analysis of cast-in-situ RC shear wall-column was carried out and compared with the performance of similar precast RC wall-connected through loop bars.

Precast RC walls are advantageous over conventional monolithic RC walls in terms of the rapid and efficient construction process, with speed, safety and economy in the construction. The effectiveness of the proposed wall systems, i.e. precast RC hollow core wall and precast wall-column connected through loop bars, is demonstrated by examining their seismic performance through displacement controlled quasi-static lateral load reversed cyclic tests following relevant standards. 

The experimental results were compared with the numerical results, which showed good agreement between the two. Precast RC wall systems demonstrated ductile behaviour with satisfactory lateral load-carrying capacity and deformation characteristics, along with remarkable energy dissipation. The research programme concluded the proposed precast RC walls to be promising in terms of strength, speed, economy and execution considerations.

 

Behaviour of Precast RC Hollow Core Wall (PHCW)

PHCW demonstrated overall ductile behaviour with no cracks on the wall surface, attributed to the well-detailed reinforcement in the wall. However, brittle damage was observed in the encompassing RC band due to compression-tension action during the test. The numerical model also demonstrated a similar damage pattern in the form of stress concentration in the encompassing RC band. Though the encompassing RC band suffered brittle damage, it was found to be effective in limiting the damage at the bottom of precast RC walls along the length. 

Steel truss elements were effective in connecting the precast panels. Fig. 2(a) shows the damage pattern in PHCW, while Fig. 3(a) shows the lateral load-displacement hysteresis curve. The wall demonstrated a lateral load-carrying capacity of 352 kN, surpassing its design load of 300 kN, thus indicating satisfactory performance. 

Moreover, superior deformation characteristics with 2.81 % drift, 5.29 ductility and 3.1 response reduction factor were obtained. These values are well comparable to the numerical results (Table 1).

 

Behaviour of Precast Wall-Column with Loop Bars (PWCL)

The Loop bar connection was found to be adequate for transferring the load between the precast wall and columns. However, grout in the joint region between the wall and column experienced cracks at higher loading. Although, this damage is repairable, wherein the cracks can be filled with the cement mortar. Fig. 2(b) illustrates the damage pattern in PHCW, while Fig. 3(b) shows the lateral load-displacement hysteresis curve. The tested wall demonstrated 388 kN lateral load-carrying capacity at 25 mm corresponding lateral displacement. The experimental results were well comparable with the numerical results, which showed 360 kN lateral load at 26 mm corresponding displacement. Table 1 summarizes the experimental and numerical results obtained.

 

Table 1: Seismic Parameters for Tested Precast RC Walls

Parameter

PHCW

PWCL

Experimental

Numerical

Experimental

Numerical

Maximum Load (kN)

352

362

388

360

Displacement at Maximum Load (mm)

27.6

29.6

24.5

26.3

Stiffness at Yield Point (kN/m)

28.75

21.8

24.28

23.8

Stiffness at Peak Load (kN/m)

12.75

12.23

15.84

13.69

Ultimate Drift (%)

2.81

2.65

2.57

2.30

Ductility

5.29

4.29

3.87

6.93

Behaviour Factor 

3.10

2.75

2.60

3.58

Energy Ratio (%)

78.88

-

84.65

-


Dr Ajay Chourasia& C. Shermi
3D-Concrete, Printing Group
CSIR-Central Building Research Institute, Roorkee