Civil Engineering Reference
In-Depth Information
a. Mechanical and material properties of lumbers used in the wood structure.
b. Degree and characteristics of the influence on strength caused by defects of wooden
components.
c. Inspection of the positions and characteristics of corrosion and pests, and relevant
analysis of their damages to the structure.
d. Temperature and humidity conditions where the wood structure is located.
e. Understanding and measurement of the chemical component containing corrosive
medium in the surroundings in which the wood structure is located.
f. Stress and deformation state of bearing members and functional modes of connections
at main joints.
(2) Elimination of hidden hazards
Before retrofitting, reasons for wood structure retrofitting must be analyzed. Crucial
issues that endanger the safety of the wood structure should be solved firstly, followed by
relevant solutions proposed to deal with other damages. Sucient consideration should be
given to the secondary damages resulting from the same causes so that the hidden hazards
can be thoroughly eliminated.
(3) Strengthening materials
The lumber and steel selected for wood structure retrofitting should conform to the rel-
evant current national standards. The connecting lumber, used for strengthening bearing
members, should be in straight grain without defects, and its water content should be strictly
controlled.
Utilization of old lumber for strengthening bearing members or reuse of old members
(wooden columns, purlins, joists, etc.) must be verified to conform to the relevant standards
anddesignrequirements.
(4) Consolidating and improving the structure load resisting system
Depending on different structure loading states, retrofitting requirements, material sup-
plies, construction sites and available construction conditions, the retrofitting of wood struc-
tures has two levels: consolidating and improving the current situation. Here the current
situation mainly refers to the conditions of structure load resisting systems.
a. Consolidating the current situation
The structure is in a good condition as a whole; however, hidden hazards may endanger
the safety and serviceability of the structure if no attention is given to them. Ecient
measures should be adopted to eliminate local hazards or control the worsening of hazards
so as to ensure safety and maintain reliability of original structure.
This level of retrofitting focuses on the wood structure itself. For example:
a) Failure of the individual members in roof trusses or braces, or damage of the clamps
at joints, can be solved by replacing with new members or plates which conform to the
standards.
b) When damages take place in some parts of members and joints, or defects in some
members are over the limit, local strengthening can be ecient to meet the safety demand.
c) If the lumber near the bearing area is eroded only on the surface and in an early stage,
with the inner layers in good condition and dry, it is feasible to remove the rotten parts
thoroughly and apply antiseptic to the surface and inner layers. Then the structure can
maintain normal service.
d) The original wooden tension rods can be replaced by steel ones, if they are disabled.
e) Skew of the roof truss or large out-of-plane deformation of individual compression rods
can be rectified by angle steels and bolts to meet the service demand. Braces may be added
when necessary.
