Which reference is incorporated for the design of vertical and horizontal forms that must be kept on-site?

The correct reference for the design of vertical and horizontal forms that must be kept on-site is the American Concrete Institute's publication titled "Formwork for Concrete." This document specifically addresses the best practices and standards for constructing formwork used in concrete applications. It covers crucial aspects such as the design, materials, and maintenance of formworks to ensure safety and structural integrity during the construction process. Since formwork is an essential part of concrete construction, having the guidelines from a specialized authority like the American Concrete Institute is crucial for contractors.

The other references do not focus specifically on formwork design. ASTM's guidelines pertain to various materials and testing methods but do not have dedicated guidelines for form design. The National Building Code Guidelines primarily address overall building safety and compliance but do not delve into specific formwork requirements. OSHA Safety Standards are centered around occupational safety and health regulations but do not provide detailed information on the design and construction of concrete formwork.