The Ashgate Books
1. Structural iron and steel, 1850-1900. Robert Thorpe. Ashgate 2000.
2. The development of timber as a structural material. David Yeomans. Ashgate 1999. (The section on manuals seems to be particularly appealing).
3.** Structural and civil engineering design. William Addis. Ashgate 1999.
4. Structural iron, 1750-1850. R.J.M. Sutherland. Ashgate 1997.
5. Early reinforced concrete. Frank Newby. Ashgate 2001.
Other references of note include Concrete by Peter Collins, and Liquid Stone.
There are a few other works that I'll have to get once the current ILL batch goes through: Proceedings of the First International Congress on Construction History and Kurrer's The History of the Theory of Structures.