Experimental Research on Fatigue Behavior of Existing Reinforced Concrete Beams

In order to obtain the law of the fatigue damage development of reinforced concrete hollow beams that has been in service for 24 years, its solid hollow beams were removed and transported to the laboratory for loading test. Two beams were selected for static loading to obtain the ultimate flexural bearing capacity, and three beams were, respectively, subjected to constant-amplitude fatigue loading with different load amplitudes. The static and dynamic behaviors of the beams were monitored in the fatigue test. The fatigue failure of the beams showed that the outermost rebar at the butt weld fractured at first, and the crack width at the fracture position of the steel bar was about 0.3 mm, which was largest in all cracks. After a rebar was broken, midspan deflection and flexibility increased by approximately 20% and 10%, respectively, relative to the initial state. The damage developed rapidly in the following range: (1) the first 10,000 fatigue cycles; (2) after fatigue fracture of the rebar; and in the intermediate stage of fatigue test, the damage development was relatively stable. As the loading amplitude increased, the stiffness degradation and the cumulative damage that occured under the same loading cycle were more significant.

Tunable Axicons Generated by Spatial Light Modulator with High-Level Phase Computer-Generated Holograms

Axicon is an interesting optical element for its optical properties. This paper presents an approach to dynamically generated tunable axicons with a spatial light modulator (SLM). 256-level phase computer-generated holograms (CGHs) were loaded into the SLM to simulate the positive and negative axicons. The intensity distributions of beams passing through these axicons were analyzed with the principle of blazed grating and Fresnel diffraction; and the diffraction patterns were obtained theoretically in terms of zero-order Bessel beams and annular hollow beams, corresponding to the positive and negative axicons, respectively. Experimental results verified that the diffraction patterns have the same distribution as the real axicon. The types of the axicon and the axicon’s parameters can be easily altered through changing the CGHs.

Numerical and Experimental Study on the Dynamic Behavior of an Innovative Steel-Concrete Composite Hollow Waffle Floor

The U-shaped steel-concrete composite hollow waffle (CHW) floor is an innovative slender large-span floor composed of a thin slab and bidirectional orthogonal steel-concrete composite hollow beams. Large vibrations may occur under human excitations, and vibration guidelines for CHW floors are still lacking. Thus, this paper undertook a parametric and experimental study to explore the vibration performance of the CHW floors. First, the modal properties and vibration response under walking tests considering the varying frequencies and routes were obtained from the measurements, which validated the accuracy of the finite element analysis (FEA). Then, the influence of the structural parameters on the floor vibration was investigated by numerical modeling. The parametric study shows that the medium-sized long-span (MLS) (28[Formula: see text]m) CHW floors present the best vibration serviceability, the small-sized long-span (SLS) (14[Formula: see text]m) CHW floors vibrate substantially under walking excitation, and the large-sized long-span (LLS) (42[Formula: see text]m) CHW floors are vulnerable to resonance. Finally, this paper provides recommendations for design guidelines for CHW floors and indicates that controlling the span-to-height (SH) value and beam spacing (BS) at a small value are the most effective methods of vibration control.