PSI - Issue 59

Olena Romashko-Maistruk et al. / Procedia Structural Integrity 59 (2024) 352–359 O. Romashko-Maistruk and V. Romashko/ Structural Integrity Procedia 00 (2023) 000 – 000

353

2

individual recommendations (CEB-FIP (1991), fib (2012)), the relationship between the type of load and the strain rate of concrete can be outlined in the table 1.

Table 1. Strain rate of concrete depending on the load type Load type

Strain rate of concrete   , s -1

10 -10 …10 -6 10 -6 …10 -5 10 -5 …10 -2 10 -3 …10 0 10 -2 …10 1 10 -1 …10 2

Long-acting (creeping)

Static, quasi-static

Collision with ships, vehicles, gas explosion

Airplane crashes, shock waves

Earthquakes

Rocket strikes, falling stones, driving piles

Strong explosions 10 -1 …10 4 Nuclear, thermonuclear and astrophysical explosions 10 2 …10 8

Dynamic

Since concrete belongs to the group of elastic-plastic materials, it is quite obvious that its main physical and mechanical characteristics (strength, modulus of elasticity, critical strains and etc.) will directly depend on the load rate or the strain rate (Fig. 1). Many researchers are still working on establishing such dependencies. However, the identification of the main regularities of these relationships is hindered by quite significant discrepancies in the experimental studies results. They usually increase with an increase in the strain rate of concrete and are caused by the following factors: • lack of uniform standardized methods of dynamic load tests; • using samples of different shapes and geometric sizes; • using test samples with different types and proportions of components, and therefore with different static strengths; • testing samples of different ages, aged in different temperature and humidity conditions; • determination of the concrete static strength at different static strain rate; • the influence of various inertial and frictional effects.

 с

f с,du

5

1

2

f c,d

3

f ck

f с,lu

4

 с

 с1,d

 с1

 сe,u

 с,lu

-1 ; 3 -

(10 ...10 ) 6 5      s -1 ; 4 -

Fig. 1. Concrete stress-strain diagrams depending on the strain rate: 1 -

   ; 2 -

(10 ...10 ) 2 2     s

; 5 -

0   

curve of limit strains.