Experimental Investigation of Axial Compression in Composite Strengthened Historical Timber Columns

ABSTRACT

This work explores the effectiveness of composite strengthening for historical timber columns, which strengthens the timber columns with near surface mounted steel bars and wrapped CFRP strips. Different numbers of steel bars and two approaches for attaching CFRP strips were compared in tests of 36 timber columns. The failure modes, ultimate load, and ductility of specimens were analyzed. The stress-strain curves and deformation compatibility of each component of specimens were discussed. The results indicate that the composite strengthening effectively enhances the ductility and bearing capacity of strengthened timber columns. Pre-tensioned CFRP strips performed better than the epoxy-bonded CFRP strips in improving the bearing capacity and compression elastic modulus, but not in enhancing deformation performance. Analysis of the strain comparison curves showed that the embedded steel bars and timber can work together in deformation, and that the wrapped CFRP strips can restrain timber columns’ lateral expansion. Overall, reliable and effective strengthening was achieved using the proposed reinforcement method. Finally, according to fitting analysis and related theories about CFRP confined concrete columns, a calculation model of peak loads for strengthened timber columns was established. The reliability of the newly proposed model was verified through the comparison between theoretical and experimental values.

KEYWORDS:

• Axial compression experiment
• epoxy-bonded CFRP strips
• near surface-mounted steel bar
• pre-tensioned CFRP strips
• strain comparison curves
• stress-strain curves

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notation list

A_c section area of timber column;

A_cj effective confinement area of CFRP strips;

b_f width of CFRP strips;

D diameter of timber columns;

E_CFRP elastic modulus of CFRP strips;

f_CFRP tensile strength of CFRP strips;

f_cc peak stress of strengthened timber columns;

f_co compression stress of unconfined timber columns;

f_l confinement stress of CFRP strips;

f_l^′ effective confinement stress of CFRP strips;

k confinement coefficient of CFRP strips;

k_s effective confinement factor;

k_ε effective strain factor;

N_u bearing capacity of strengthened timber columns;

P_u peak load of tested specimens;

${\bar{P}}_u$ average peak load of each group of tested specimens;

S_cj spacing of adjacent CFRP strips;

t_f thickness of CFRP strips;

u_Δ ductility coefficient of tested specimens;

${\bar{u}}_{\mathrm{\Delta }}$ average ductility coefficient of each group of tested specimens;

ε_CFRP ultimate tensile strain of CFRP strips;

Δ_y nominal yield displacement of tested specimens;

Δ_u ultimate displacement of tested specimens;

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (Grant number 52078030, 51678039).