I recently had a productive meeting with Eddy Ruble regarding the use of ICEBs as an alternate construction method here in West Sumatra. I have had considerable experience with such blocks (albeit a different design) in various African countries. At a recent Early Recovery Cluster group meeting I introduced the concept and received some strong interests, including from the Public Works department.
To move forward with this method, I need to provide 'doubters' with answers to two questions, namely:
- how resistant are the blocks to the heavy rains encountered in West Sumatra? (we have used them in southern Sudan and uganda which also have heavy rainy seasons); and
- how do they stand up to 8.0 earthquake shaking?
HAve the blocks ever been tested on shake-tables? If so, where?
Well designed and built earth buildings have a good history of water and earthquake resistance. The Franciscans built their missions of unstabilized adobe in earthquake prone California. Most of them are still standing today, some 400 years later.
For water resistance, architects give us the saying that a good earth house needs good boots and a good hat. That is, it needs an anti-capillary layer to prevent sucking up of water from the ground as well as plastering the first few courses to prevent against splashing erosion. It also needs a good roof with some overhang to prevent rain from repeatedly hitting on top of a block. If you use thatch, you need to maintain it.
For earthquake resistance we need adequate reinforcement. ICEBs are reinforceable horizontally and vertically internally. ICEBs have been used for about 25 years in South East Asia and many other places. They've been used in Sumatra for at least 3 years.
There was some testing done on a block wall at the Structural Engineering and Construction Lab of the Asian Institute of Technology near Bangkok. The Thailand Institute for Scientific and Technological Research has done load testing on block pillars. California Polytechnic State University, San Luis Obispo will be doing a shear wall test this school year.
The earthquake resistance of a building is often dependent on how it is designed and how it is anchored and reinforced. Good earthquake resistant design principles are the same for any building material or system.
Hydraform in SA have run some severe quake shake table tests. (http://www.hydraform.com/BuildingSystems/Earthquake.asp) You can watch the video. The test "room" was dry stack and unreinforced ungrouted from what I can see. (correct me if I am wrong)
They used a small concrete ring beam at the top of the wall but it seems that they did not include any other reinforcing or post stack grouting. (maybe a lintel block of some kind?) The quakes were from just below to over 7 so of the order that we can now expect here.
For ICEB block system I am thinking we could use:
Intermediate channel block with 1 x 8mm deformed bar ring reinforcing at base of wall, at window sill height and at window and door head height.
2 x 8mm deformed vertical reinforcing at corners, same at mid wall (3m or more) and end piers, 1 x 8mm deformed bar either side of windows and doors or where we have roof trusses to tie down.
PLUS double horizontal channel block ring beams with 1 x 8mm deformed bar that is continuous at the top of the wall (one above the other)
1 x 8mm deformed bar corner stirrups to tie walls together at all horizontal reinforced courses
8mm plain bar diagonal bracing at bottom chord of roof trusses so the roof will stiffen the walls rather than load them (quake loads)
my feeling is that we would be well above the strength required for domestic construction in WS. I am assuming a lot so would like your thoughts please.
I am trying to avoid the need to form and cast a reinforced concrete beam if possible. We have proven that diagonal roof bracing is very effective for bracing walls. (more info on request)
I think if you look around on their site you'll find that Hydraform did reinforce with vertical and horizontal single bars.
Although the bottom cord of a roof truss with diagonal bracing will reinforce and stabilize a wall, I suspect that the structural engineers would like us to have a beam with 2 horizontally parallel rebars (side by side) with stirups. This can be done with our current channel block with 6 mm rebar (perhaps 8 as well). I believe we can make a channel block with a wider channel by using a high-cement mix. Would this satisfy your desire to not use formwork? There are some test reports on ICEB channel block beam capacities although I haven't looked at them yet. Perhaps they would tell us something about the lateral bending moment capacity of channel block beams.
We would be delighted to use a larger frog so that the channel block could take 2 steel bars and stirrups. We will still use the roof truss bracing because we have seen what a big difference it makes in our own bungalow. We had quite bad cracking in wall panels on our long walls during the 2007 quakes and frankly we realized that they were not well enough braced and had too many openings. I was worried that the next quake would bring the walls down. We braced with 7mm plain rod and this recent quake cause far less damage than the previous much lower intensity quakes did. This idea is definitely effective and low cost. It converts the entire roof truss metal deck roof structure into a horizontal bracing plane to eliminate horizontal loads from the middle truss causing damage to the long walls. I can send photos if there is a way to post them here.