A column assembly has an elongated tubular member. A wall end assembly has an elongated tubular member. A flexible interface connects the column assembly to the wall end assembly. The flexible interface includes a spring pack assembly having a disc spring, an elongated male fastening member, a female fastening member, and an absorbing layer. The male fastening member extends through the spring pack hole into the female fastening member to connect the column assembly to the wall end assembly with the female fastening member and to hold the male fastening member in place.