Civil Engineering Reference
In-Depth Information
diameters of holes should not be larger than those of the shear bolts by 1 mm, or larger
than the fastening bolts by 2 mm.
The splices of the round steel tension bars for retrofitting should be welded by double ties.
The diameter of the round steel tie ought to be no less than 0.75 times that of the tension
bar. The tie length on one side of splice should be no shorter than 5 times the diameter of
tension bar.
(7) Seismic strengthening of wood structures
a. Seismic checking calculations are not necessary in seismic strengthening of wood struc-
tures.
b. Seismic capacities of wood frames should be improved by strengthening. Based on
actual condition, some ecient measures can be adopted such as reducing roof weight,
strengthening wood frame, reinforcing joints, adding column bracings and brick walls and
so on. The column bracings and seismic walls should be set uniformly in floor plane.
Bearing systems are the key points of seismic strengthening.
5.2
Retrofitting of Wooden Beams
1. Strengthening with clamped or haunched connection methods
The supporting points (the ends connected with walls) of wooden beams are vulnerable to
decay, corrosion and other damages. It is reliable to adopt clamped or haunched connection
methods to strengthen the wooden beams in these cases. If the damage depth on the upper
or bottom sides of the beam is larger than 1/3 of its height, it should be strengthened with
clamps. Otherwise, if damage depth is larger than 3/5 of the height, the beam-end should
be replaced by a new one. If the beam-end is moth-eaten, it can also be strengthened with
clamps according to calculation.
Before strengthening, the beams should be supported temporarily or unloaded. The
supporting points should be in alignment when the beams are within different stories. The
damaged parts of the supported beams should be cut off before strengthening with the
methods mentioned above.
(1) Clamped connection
Beams can be strengthened with clamped connections
(Fig. 5.2)
.
The cross section and
M
1
M
2
R
1
R
2
S
Fig. 5.2
Strengthening of wooden beam with clamped connection.
