CVEN90017 Earthquake Resistant Design of Buildings.

CVEN90017 Earthquake Resistant Design of Buildings

Assignment no.2

Seismic Assessment of Reinforced Concrete Walls

Year 2021

(Due on Sunday 30th of May at 11:59 pm) students may work individually or in pairs

Consider the floor plan of a multi-storey building in the next page. The structural engineer has designed the gravity frame (i.e., beams, columns, and slabs), but has yet to design the reinforced concrete core to resist the lateral loads. It is assumed for this assignment that earthquake loading, rather than the loading from wind, governs the design. Your task is to design a reinforced concrete core wall to resist the earthquake loading designed to AS 1170.4. You then need to calculate the displacement-capacity of the wall by first conducting a moment-curvature analysis (or sectional analysis), and conduct seismic assessment of the core walls using the capacity spectrum method. The following can be assumed for the building:

? The building has a total height (Hn) of 42 meters.

? The building has 12 floors with an inter-storey height of 3.5 meters.

? The building is designed for a superimposed dead load of 1 kPa and live load of 3 kPa. The thickness of the slab is 240 mm, the self weight of other structural elements can be ignored in the calculation of dead load.

? It can be assumed that the building is torsionally-symmetrical and that higher mode effects do not need to be considered.

? The wall geometry must fit within the area designated below in the floor plan.

? The wall is assumed to be of uniform cross-section up the height of the structure.

? It can be assumed that the “razor” columns do not contribute to the structure’s lateral stiffness

? In conducting the moment-curvature analysis, you may assume axial load ratio of 5%

Figure 1 Building Plan Layout with area for designed core wall/s

Task no. 1

Design a core wall to resist the lateral load determined from the Earthquake Loading Australian

Standard AS1170.4. You can assume the building is located in Melbourne (Z=0.08g) and 500 yr RP. The building is situated on Class D site conditions. You should make sure that the core wall/s have sufficient strength to resist the ground motions in both translational directions.

Task no. 2

The class has been trained on the use of EXCEL spreadsheets for undertaking analysis of the moment-curvature relationship of rectangular cross-sections. You are required to further develop and make use of your own designed spreadsheets for developing the moment-curvature relationships of the concrete cross-section at the base of the structural walls that you have designed. You are required to develop two curves, one curve with on an unconfined concrete model and one with a confined concrete model.

It is important that you undertake independent checks over the accuracies of the spreadsheet that you have created. The checking may be accomplished by comparing results from software that can be downloaded free from the internet. A well-known example of such software is RESPONSE-2000.

You should determine the following with your EXCEL sectional-analyses program:

? Curvature and moment at first yield (i.e., when the steel in the extreme tension fibre region first reaches the yield strain)

? Curvature and moment at ultimate (i.e., when the moment is at a maximum, or when the compression strain reaches an ultimate unconfined strain of 0.003)

The moment-curvature curve of the section can be plotted by investigating the moment and curvature for different levels of reference strain up until failure. “Failure” is defined here as when the ultimate tension (esu = 0.060) or compression (ecu = 0.003 or ecc = 0.010) strains are reached, or when a 20% drop in strength (i.e., moment) has occurred from its maximum. If the wall is non-rectangular, one-direction of bending can be assessed, rather than multiple (i.e., the

“weaker” direction, or bending about the weaker [minor] axis, for example).

Task no. 3

Determine the displacement-capacity of the core wall/s. You should use the equations given in the lecture for a plastic hinge analysis. Furthermore, you should also compare the displacement capacity of the building with the following assumptions:

? A single, primary crack forms and the equivalent plastic hinge length (Lp) is limited to a small height at the base.

? Secondary cracking occurs and the equivalent plastic hinge length (Lp) can form some height up the wall from the base of the unconfined wall.

? Secondary cracking occurs and the equivalent plastic hinge length (Lp) can form some height up the wall from the base of the confined wall.

Task no. 4

Based on the three assumptions made in Task 3, assess if the building is safe under a very rare event (2500 yr return period earthquake) on site class D site. You may use the capacity spectrum method to undertake the assessment. The acceleration displacement response spectrum demand should be constructed based on site specific analysis using the MatLab program available in QuakeAdvice. The bore hole information can be downloaded from Canvas – Module – Assignment 2 Bore hole information.