How strong are chimpanzees?

They are much stronger than humans, partly because their muscles are attached to the bones differently than ours, giving them more mechanical advantage than we have. For example, your biceps are attached to the bone about an inch from the joint, while a chimp's bicep is attached farther from the joint, allowing it to have more strength, despite the smaller size and the smaller muscles. This difference holds true throughout the comparisons between people and chimps. This is why, even though they are about half our size, they can rip us apart if they want to.